Remove the ability to save backups to the external SD card.

The directory we were previously saving backups to on the external SD
card is actually deleted upon app uninstall and/or clearing the app's
data. There's also no reliable way to write to the root of an external
SD card (that isn't comically inconvenient), so for now it's safer if we
just move back to getting the regular 'ol standard external storage
directory (which is likely internal storage, despite its name).

Fixes #7845

src/org/thoughtcrime/securesms/RegistrationActivity.java

@@ -318,7 +318,7 @@ public class RegistrationActivity extends BaseActionBarActivity implements Verif
       @Override
       protected @Nullable BackupUtil.BackupInfo doInBackground(Void... voids) {
         try {
-          return BackupUtil.getLatestBackup(RegistrationActivity.this);
+          return BackupUtil.getLatestBackup();
         } catch (NoExternalStorageException e) {
           Log.w(TAG, e);
           return null;

src/org/thoughtcrime/securesms/backup/BackupDialog.java

@@ -77,7 +77,7 @@ public class BackupDialog {
                    .setPositiveButton(R.string.BackupDialog_delete_backups_statement, (dialog, which) -> {
                      TextSecurePreferences.setBackupPassphrase(context, null);
                      TextSecurePreferences.setBackupEnabled(context, false);
-                     BackupUtil.deleteAllBackups(context);
+                     BackupUtil.deleteAllBackups();
                      preference.setChecked(false);
                    })
                    .create()

src/org/thoughtcrime/securesms/jobs/LocalBackupJob.java

@@ -52,7 +52,7 @@ public class LocalBackupJob extends ContextJob {
 
     try {
       String backupPassword  = TextSecurePreferences.getBackupPassphrase(context);
-      File   backupDirectory = StorageUtil.getBackupDirectory(context);
+      File   backupDirectory = StorageUtil.getBackupDirectory();
       String timestamp       = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss", Locale.US).format(new Date());
       String fileName        = String.format("signal-%s.backup", timestamp);
       File   backupFile      = new File(backupDirectory, fileName);
@@ -78,7 +78,7 @@ public class LocalBackupJob extends ContextJob {
         throw new IOException("Renaming temporary backup file failed!");
       }
 
-      BackupUtil.deleteOldBackups(context);
+      BackupUtil.deleteOldBackups();
     } finally {
       GenericForegroundService.stopForegroundTask(context);
     }

src/org/thoughtcrime/securesms/util/BackupUtil.java

@@ -22,7 +22,7 @@ public class BackupUtil {
 
   public static @NonNull String getLastBackupTime(@NonNull Context context, @NonNull Locale locale) {
     try {
-      BackupInfo backup = getLatestBackup(context);
+      BackupInfo backup = getLatestBackup();
 
       if (backup == null) return context.getString(R.string.BackupUtil_never);
       else                return DateUtils.getExtendedRelativeTimeSpanString(context, locale, backup.getTimestamp());
@@ -32,8 +32,8 @@ public class BackupUtil {
     }
   }
 
-  public static @Nullable BackupInfo getLatestBackup(@NonNull Context context) throws NoExternalStorageException {
+  public static @Nullable BackupInfo getLatestBackup() throws NoExternalStorageException {
-    File       backupDirectory = StorageUtil.getBackupDirectory(context);
+    File       backupDirectory = StorageUtil.getBackupDirectory();
     File[]     backups         = backupDirectory.listFiles();
     BackupInfo latestBackup    = null;
 
@@ -49,9 +49,9 @@ public class BackupUtil {
   }
 
   @SuppressWarnings("ResultOfMethodCallIgnored")
-  public static void deleteAllBackups(@NonNull Context context) {
+  public static void deleteAllBackups() {
     try {
-      File   backupDirectory = StorageUtil.getBackupDirectory(context);
+      File   backupDirectory = StorageUtil.getBackupDirectory();
       File[] backups         = backupDirectory.listFiles();
 
       for (File backup : backups) {
@@ -62,9 +62,9 @@ public class BackupUtil {
     }
   }
 
-  public static void deleteOldBackups(@NonNull Context context) {
+  public static void deleteOldBackups() {
     try {
-      File   backupDirectory = StorageUtil.getBackupDirectory(context);
+      File   backupDirectory = StorageUtil.getBackupDirectory();
       File[] backups         = backupDirectory.listFiles();
 
       if (backups != null && backups.length > 2) {

src/org/thoughtcrime/securesms/util/StorageUtil.java

@@ -14,20 +14,8 @@ import java.io.File;
 
 public class StorageUtil {
 
-  public static File getBackupDirectory(Context context) throws NoExternalStorageException {
+  public static File getBackupDirectory() throws NoExternalStorageException {
-    File storage = null;
+    File storage = Environment.getExternalStorageDirectory();
-
-    if (Build.VERSION.SDK_INT >= 19) {
-      File[] directories = context.getExternalFilesDirs(null);
-
-      if (directories != null) {
-        storage = getNonEmulated(directories);
-      }
-    }
-
-    if (storage == null) {
-      storage = Environment.getExternalStorageDirectory();
-    }
 
     if (!storage.canWrite()) {
       throw new NoExternalStorageException();
@@ -46,27 +34,9 @@ public class StorageUtil {
   }
 
   public static File getBackupCacheDirectory(Context context) {
-    if (Build.VERSION.SDK_INT >= 19) {
-      File[] directories = context.getExternalCacheDirs();
-
-      if (directories != null) {
-        File result = getNonEmulated(directories);
-        if (result != null) return result;
-      }
-    }
-
     return context.getExternalCacheDir();
   }
 
-  private static @Nullable File getNonEmulated(File[] directories) {
-    return Stream.of(directories)
-                 .withoutNulls()
-                 .filterNot(f -> f.getAbsolutePath().contains("emulated"))
-                 .limit(1)
-                 .findSingle()
-                 .orElse(null);
-  }
-
   private static File getSignalStorageDir() throws NoExternalStorageException {
     final File storage = Environment.getExternalStorageDirectory();