refactor: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

Reference: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

safesocket/safesocket_darwin.go

@@ -9,7 +9,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -70,7 +69,7 @@ func localTCPPortAndTokenDarwin() (port int, token string, err error) {
 		// The current binary (this process) is sandboxed. The user is
 		// running the CLI via /Applications/Tailscale.app/Contents/MacOS/Tailscale
 		// which sets the TS_MACOS_CLI_SHARED_DIR environment variable.
-		fis, err := ioutil.ReadDir(dir)
+		fis, err := os.ReadDir(dir)
 		if err != nil {
 			return 0, "", err
 		}