Remove nonEnumShadows.

lodash.js

@@ -1483,9 +1483,6 @@
     /** Used to store function metadata. */
     var metaMap = WeakMap && new WeakMap;
 
-    /** Detect if properties shadowing those on `Object.prototype` are non-enumerable. */
-    var nonEnumShadows = !propertyIsEnumerable.call({ 'valueOf': 1 }, 'valueOf');
-
     /** Used to lookup unminified function names. */
     var realNames = {};
 
@@ -11147,7 +11144,7 @@
       if (tag == mapTag || tag == setTag) {
         return !value.size;
       }
-      if (nonEnumShadows || isPrototype(value)) {
+      if (isPrototype(value)) {
         return !nativeKeys(value).length;
       }
       for (var key in value) {
@@ -12245,7 +12242,7 @@
      * // => { 'a': 1, 'c': 3 }
      */
     var assign = createAssigner(function(object, source) {
-      if (nonEnumShadows || isPrototype(source) || isArrayLike(source)) {
+      if (isPrototype(source) || isArrayLike(source)) {
         copyObject(source, keys(source), object);
         return;
       }