Simplify default export

This removes unnecessary variable declarations where the default object is an object.

src/ol/layer/TileProperty.js

@@ -1,12 +1,11 @@
 /**
  * @module ol/layer/TileProperty
  */
+
 /**
  * @enum {string}
  */
-var _ol_layer_TileProperty_ = {
+export default {
   PRELOAD: 'preload',
   USE_INTERIM_TILES_ON_ERROR: 'useInterimTilesOnError'
 };
-
-export default _ol_layer_TileProperty_;