fix(android) don't re-launch activity after closing PiP

Just remain in the background. The ongoing notification can be used to
get back to the meeting.

NOTE: This behavior only affected the app, not the SDK.

android/app/src/main/java/org/jitsi/meet/MainActivity.java

@@ -211,11 +211,6 @@ public class MainActivity extends JitsiMeetActivity {
         super.onPictureInPictureModeChanged(isInPictureInPictureMode);
 
         Log.d(TAG, "Is in picture-in-picture mode: " + isInPictureInPictureMode);
-
-        if (!isInPictureInPictureMode) {
-            this.startActivity(new Intent(this, getClass())
-                .addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT));
-        }
     }
 
     // Helper methods