Android: Removed empty onDraw() override method from SDLActivity.

It was redundant because SDLActivity already inherits an empty method from the
base class SurfaceView (which does not implement it but inherits it from View).
Visibility of onDraw() in SDLActivity is now protected again instead of public.

android-project/src/org/libsdl/app/SDLActivity.java

@@ -1136,11 +1136,6 @@ public void run(){
         }
     }
 
-    // unused
-    @Override
-    public void onDraw(Canvas canvas) {}
-
-
     // Key events
     @Override
     public boolean onKey(View  v, int keyCode, KeyEvent event) {