rn: enable auto-pinning on screenshare on mobile

react/features/video-layout/subscriber.js

 declare var APP: Object;
 declare var interfaceConfig: Object;
 
+// TODO: interfaceConfig should be in redux so we didn't have to do this.
+const AUTO_PIN_LATEST_SCREEN_SHARE
+    = typeof interfaceConfig === 'object' ? interfaceConfig.AUTO_PIN_LATEST_SCREEN_SHARE : 'remote-only';
+
 /**
  * StateListenerRegistry provides a reliable way of detecting changes to
  * preferred layout state and dispatching additional actions.
             dispatch(
                 setMaxReceiverVideoQuality(VIDEO_QUALITY_LEVELS.HIGH));
 
-            if (typeof interfaceConfig === 'object'
-                && interfaceConfig.AUTO_PIN_LATEST_SCREEN_SHARE) {
+            if (AUTO_PIN_LATEST_SCREEN_SHARE) {
                 _updateAutoPinnedParticipant(store);
             }
         }
 StateListenerRegistry.register(
     /* selector */ state => state['features/base/tracks'],
     /* listener */ (tracks, store) => {
-        if (typeof interfaceConfig !== 'object'
-            || !interfaceConfig.AUTO_PIN_LATEST_SCREEN_SHARE) {
+        if (!AUTO_PIN_LATEST_SCREEN_SHARE) {
             return;
         }
 
         const knownSharingParticipantIds = tracks.reduce((acc, track) => {
             if (track.mediaType === 'video' && track.videoType === 'desktop') {
                 const skipTrack
-                    = interfaceConfig.AUTO_PIN_LATEST_SCREEN_SHARE === 'remote-only'
-                        && track.local;
+                    = AUTO_PIN_LATEST_SCREEN_SHARE === 'remote-only' && track.local;
 
                 if (!skipTrack) {
                     acc.push(track.participantId);