rn,filmstrip: don't unpin participant when hiding filmstrip

The filmstrip is currently only hidden when PiP mode is entered. There is no
real reason not to leave the large view as it was.

react/features/filmstrip/middleware.js

 // @flow
 
 import { setLastN } from '../base/conference';
-import { pinParticipant } from '../base/participants';
 import { MiddlewareRegistry } from '../base/redux';
 
 import { SET_FILMSTRIP_ENABLED } from './actionTypes';
 function _setFilmstripEnabled({ dispatch, getState }, next, action) {
     const result = next(action);
 
-    // FIXME The logic for participant pinning / unpinning is not on React yet
-    // so dispatching the action is not enough. Hence, perform the following
-    // only where it will be sufficient i.e. mobile.
+    // FIXME This action is not currently dispatched on web.
     if (typeof APP === 'undefined') {
         const state = getState();
         const { enabled } = state['features/filmstrip'];
         const { audioOnly } = state['features/base/conference'];
 
-        enabled || dispatch(pinParticipant(null));
-
         // FIXME Audio-only mode fiddles with lastN as well. That's why we don't
         // touch lastN in audio-only mode. But it's not clear what the value of
         // lastN should be upon exit from audio-only mode if the filmstrip is