Revert "FIX: simpler w function check (#7496)"

This reverts commit 2570311718.

vendor/assets/javascripts/i18n-patches.js

@@ -13,7 +13,7 @@
       return oldI18ntoHumanSize.apply(this, [number, options]);
     };
 
-    if ("w" in String.prototype) {
+    if (Ember.typeOf(String.prototype.w) === "function") {
       String.prototype.i18n = function(options) {
         return I18n.t(String(this), options);
       };