[Android] Clean up AboutFragment's onAttach method.

Source/Android/src/org/dolphinemu/dolphinemu/AboutFragment.java

@@ -52,16 +52,7 @@ public void onAttach(Activity activity)
 	{
 		super.onAttach(activity);
 
-		// This makes sure that the container activity has implemented
-		// the callback interface. If not, it throws an exception
-		try
-		{
-			m_activity = activity;
-		}
-		catch (ClassCastException e)
-		{
-			throw new ClassCastException(activity.toString()
-					+ " must implement OnGameListZeroListener");
-		}
+		// Cache the activity instance.
+		m_activity = activity;
 	}
 }