Delete (or modify) _correlation_cost test cases

[facaiy]

As _correlation_cost became private method, we might should remove those related test cases.

[fsx950223]

As _correlation_cost became private method, we might should remove those related test cases.

Good idea.Maybe I can fix the test case later.

[seanpmorgan]

Agree... though I would request that they be modified so the same test coverage is applied to the Keras Layer.

--EDIT---

Looks like the PR already does this. Thanks @fsx950223!