android: simplify code

- No need to handle the activity result in the fragment, since we already do in
  the Activity
- Automagically ddispose the view when destroyed

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetFragment.java

         return view;
     }
 
-    @Override
-    public void onActivityResult(int requestCode, int resultCode, Intent data) {
-        JitsiMeetActivityDelegate.onActivityResult(
-                getActivity(), requestCode, resultCode, data);
-    }
-
-    @Override
-    public void onDestroyView() {
-        if (view != null) {
-            view.dispose();
-            view = null;
-        }
-
-        super.onDestroyView();
-    }
-
     @Override
     public void onDestroy() {
         super.onDestroy();

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetView.java

     protected void onExternalAPIEvent(String name, ReadableMap data) {
         onExternalAPIEvent(LISTENER_METHODS, name, data);
     }
+
+    @Override
+    protected void onDetachedFromWindow() {
+        dispose();
+        super.onDetachedFromWindow();
+    }
 }