Simplify naming

react/features/base/media/components/AbstractVideoTrack.js

 
         return (
             <Video
-                mirror = { videoTrack && videoTrack.mirrorVideo }
+                mirror = { videoTrack && videoTrack.mirror }
                 onPlaying = { this._onVideoPlaying }
                 stream = { stream }
                 zOrder = { this.props.zOrder } />

react/features/base/tracks/actions.js

             type => dispatch(trackVideoTypeChanged(track, type)));
 
         // participantId
+        const local = track.isLocal();
         let participantId;
 
-        if (track.isLocal()) {
+        if (local) {
             const participant = getLocalParticipant(getState);
 
             if (participant) {
             type: TRACK_ADDED,
             track: {
                 jitsiTrack: track,
-                local: track.isLocal(),
+                local,
                 mediaType: track.getType(),
-                mirrorVideo: _shouldMirror(track),
+                mirror: _shouldMirror(track),
                 muted: track.isMuted(),
                 participantId,
                 videoStarted: false,

react/features/base/tracks/reducer.js

  * instance.
  * @property {boolean} local=false - If track is local.
  * @property {MEDIA_TYPE} mediaType=false - Media type of track.
- * @property {boolean} mirrorVideo=false - If video track should be mirrored.
+ * @property {boolean} mirror=false - The indicator which determines whether the
+ * display/rendering of the track should be mirrored. It only makes sense in the
+ * context of video (at least at the time of this writing).
  * @property {boolean} muted=false - If track is muted.
  * @property {(string|undefined)} participantId - ID of participant whom this
  * track belongs to.