Simplify default export

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

src/ol/ImageState.js

@@ -1,14 +1,13 @@
 /**
  * @module ol/ImageState
  */
+
 /**
  * @enum {number}
  */
-var _ol_ImageState_ = {
+export default {
   IDLE: 0,
   LOADING: 1,
   LOADED: 2,
   ERROR: 3
 };
-
-export default _ol_ImageState_;