rn,filmstrip: ignore the 'visible' parameter on mobile

Mobile uses a different logic for deciding whether to show the filmstrip or not:
if there are more than 1 participants or not, and there is no way to manually
toggle it.

react/features/filmstrip/functions.native.js

     const state = toState(stateful);
     const { length: participantCount } = state['features/base/participants'];
 
-    return state['features/filmstrip'].visible && participantCount > 1;
+    return participantCount > 1;
 }