Layouts' default background replaced with a proper theme level window background.

Bottom sheet style unified.

res/layout-sw400dp/activity_display_name.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:orientation="vertical">
 
     <View

res/layout-sw400dp/activity_landing.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:orientation="vertical">
 
     <View

res/layout-sw400dp/activity_pn_mode.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:orientation="vertical">
 
     <View

res/layout-sw400dp/activity_register.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:orientation="vertical">
 
     <View

res/layout-sw400dp/activity_restore.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:orientation="vertical">
 
     <View

res/layout-sw400dp/activity_seed.xml

@@ -3,7 +3,6 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:gravity="center_horizontal"
     android:orientation="vertical">
 

res/layout-sw400dp/fragment_enter_chat_url.xml

@@ -4,7 +4,6 @@
     android:id="@+id/contentView"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:gravity="center_horizontal"
     android:orientation="vertical">
 

res/layout-sw400dp/fragment_enter_public_key.xml

@@ -4,7 +4,6 @@
     android:id="@+id/contentView"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@drawable/default_session_background"
     android:gravity="center_horizontal"
     android:orientation="vertical">
 

res/layout-sw400dp/fragment_multi_device_removal_bottom_sheet.xml

@@ -1,42 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<LinearLayout
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto"
-    android:layout_width="match_parent"
-    android:layout_height="wrap_content"
-    android:orientation="vertical"
-    android:gravity="center_horizontal"
-    android:paddingLeft="@dimen/very_large_spacing"
-    android:paddingTop="@dimen/large_spacing"
-    android:paddingRight="@dimen/very_large_spacing"
-    android:paddingBottom="@dimen/very_large_spacing"
-    app:behavior_hideable="true"
-    app:layout_behavior="com.google.android.material.bottomsheet.BottomSheetBehavior"
-    android:background="@drawable/default_bottom_sheet_background_inset">
-
-    <TextView
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:text="Changes to Multi-Device"
-        android:textColor="@color/text"
-        android:textStyle="bold"
-        android:textSize="@dimen/very_large_font_size" />
-
-    <TextView
-        android:id="@+id/explanationTextView"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:layout_marginTop="@dimen/large_spacing"
-        android:text="You’re seeing this because you have a secondary device linked to your Session ID. To improve reliability and stability, we’ve decided to temporarily disable Session’s multi-device functionality. Device linking has been disabled, and existing secondary clients will be erased on %s.\n\nTo read more about this change, visit the Session FAQ at getsession.org/faq"
-        android:textColor="@color/text"
-        android:textSize="@dimen/small_font_size" />
-
-    <Button
-        style="@style/MediumProminentOutlineButton"
-        android:id="@+id/okButton"
-        android:layout_width="240dp"
-        android:layout_height="@dimen/medium_button_height"
-        android:layout_marginTop="@dimen/large_spacing"
-        android:text="@string/ok" />
-
-</LinearLayout>