unused code removed

frontend-js/src/main/js/map/marker/MarkerSurfaceCollection.js

 "use strict";
 
-var AbstractMarker = require('./AbstractMarker');
 var AliasMarker = require('./AliasMarker');
 var IdentifiedElement = require('../data/IdentifiedElement');
 var PointMarker = require('./PointMarker');
@@ -238,7 +237,6 @@ MarkerSurfaceCollection.prototype.removeUnmodifiedSurfaces = function (modifiedM
   var surfaceOverlaysPerType = this._overlaySurfaces[dbOverlay.getName()];
   for (var key in surfaceOverlaysPerType) {
     if (surfaceOverlaysPerType.hasOwnProperty(key)) {
-      var mapOverlay = surfaceOverlaysPerType[key];
       if (!modifiedSurfaces[key]) {
         surfaceOverlaysPerType[key].setMap(null);
         delete surfaceOverlaysPerType[key];