[BUGFIX beta] Remove use strict mode for Object.create usage.

Work around the bug identified in https://bugs.webkit.org/show_bug.cgi?id=138038,
by removing `'use strict';` from modules where `Object.create` is called
directly (in the case of `Ember.CoreObject` this occurs after inlining).
Merge pull request #9410 from rwjblue/remove-use-strict

[BUGFIX beta] Remove use strict mode for Object.create usage.