some cleanup of CoreObject

[krisselden]

No description provided.

[rwjblue]

Test failed: Mixin#reopen:  using reopen() and calling _super where there is not a super function does not cause infinite recursion
    Failed assertion: expected: Breakfast!, but was: Your breakfast was interrupted by an infinite stack error.
    at _class.testUsingReopenAndCalling_superWhereThereIsNotASuperFunctionDoesNotCauseInfiniteRecursion [as @test using reopen() and calling _super where there is not a super function does not cause infinite recursion] (http://localhost:13141/ember-tests.js:46147:14)
    at Object.<anonymous> (http://localhost:13141/ember-tests.js:82042:31)
    at runTest (http://localhost:13141/qunit/qunit.js:1478:30)
    at Test.run (http://localhost:13141/qunit/qunit.js:1464:6)
    at http://localhost:13141/qunit/qunit.js:1670:12
    at Object.advance (http://localhost:13141/qunit/qunit.js:1116:26)

[rwjblue]

Now that the PR moving weakset polyfill into Ember-utils package has landed, I think this can be updated

[rwjblue]

@krisselden - I'd hate to lose track of these changes, anything I can do to help?

[krisselden]

this is superseded by #16757