Suppress warning for the new Activity library. (#49046)

Context: cl/582573869

Author: chingjun

shell/platform/android/io/flutter/app/FlutterFragmentActivity.java

@@ -151,6 +151,7 @@ protected void onNewIntent(Intent intent) {
   }
 
   @Override
+  @SuppressWarnings("MissingSuperCall")
   public void onUserLeaveHint() {
     eventDelegate.onUserLeaveHint();
   }

shell/platform/android/io/flutter/embedding/android/FlutterFragmentActivity.java

@@ -636,6 +636,7 @@ public void onRequestPermissionsResult(
   }
 
   @Override
+  @SuppressWarnings("MissingSuperCall")
   public void onUserLeaveHint() {
     flutterFragment.onUserLeaveHint();
   }