[Bug] Private DNS shows odd message about Bluetooth

-Private DNS dialog uses preference_widget_dialog_summary
layout. It is wrong to set Bluetooth string for it.
-Remove default string from preference_widget_dialog_summary
-Set the customized string in BaseBluetoothDialogPreference

Bug: 179329046
Test: manual test
Change-Id: I749647f48e4bba7d4d0f9099d1c40d788778c15e

res/layout/preference_widget_dialog_summary.xml

@@ -18,7 +18,6 @@
 
 <TextView
     xmlns:android="http://schemas.android.com/apk/res/android"
-    android:text="@string/bluetooth_select_a2dp_codec_type_help_info"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:layout_marginTop="@dimen/developer_option_dialog_margin_top"

src/com/android/settings/development/bluetooth/BaseBluetoothDialogPreference.java

@@ -97,10 +97,14 @@ public abstract class BaseBluetoothDialogPreference extends CustomDialogPreferen
             radioButton.setText(mRadioButtonStrings.get(i));
             radioButton.setEnabled(selectableIndex.contains(i));
         }
-        // View will be invisible when all options are enabled.
+        // Initial help information text view
+        final TextView helpTextView = view.findViewById(R.id.bluetooth_audio_codec_help_info);
         if (selectableIndex.size() == mRadioButtonIds.size()) {
-            final TextView helpTextView = view.findViewById(R.id.bluetooth_audio_codec_help_info);
+            // View will be invisible when all options are enabled.
             helpTextView.setVisibility(View.GONE);
+        } else {
+            helpTextView.setText(R.string.bluetooth_select_a2dp_codec_type_help_info);
+            helpTextView.setVisibility(View.VISIBLE);
         }
     }