[BUGFIX release] Properly strip debug statements in prod builds.

In #11367 we swapped to using
babel for module transpilation, which lead to the transpiled output
being slightly different than previously with esperanto.

The long term solution is to use a babel transform to strip, this will
have the benefit of not having this particular issue any longer (this is
actually the second time we have had this issue).
https://github.com/ember-cli/babel-plugin-filter-imports has been
created specifically for this purpose, and we have a roadmap to
implementing soonish.

---

This adds the new formats to the list of debug statements for
defeatureify.

features.json

@@ -35,6 +35,16 @@
     "Ember.Logger.info",
     "Ember.default.Logger.info",
     "Ember.runInDebug",
-    "Ember.default.runInDebug"
+    "Ember.default.runInDebug",
+    "_emberMetalCore.default.deprecate",
+    "_emberMetalCore.default.warn",
+    "_emberMetalCore.default.assert",
+    "_emberMetalCore.default.debug",
+    "_emberMetalCore.default.runInDebug",
+    "_emberMetal.default.deprecate",
+    "_emberMetal.default.warn",
+    "_emberMetal.default.assert",
+    "_emberMetal.default.debug",
+    "_emberMetal.default.runInDebug"
   ]
 }