TST: Remove assertEquals

[sinhrks]

Same as #7165. I've also added some of these tests :(

One idea to prevent this is to override ``tm.TestCase.assertEquals` to raise more explicit warning or exception.

[jreback]

@sinhrks while don't we just make assertEquals == assertEqual (with a warning) though

[sinhrks]

Made suggested changes based on the unittest doc. Used deprecate decorator as a function because it can't used in the class definition.

Followings are not changed.

• assertRegexpMatches: Inroduced in python 3.1 and not used in the script. No need to be cared.
• assertRaisesRegexp: Introduced in python 3.1, but uses original implementation in util.testing. Thus untouched.

[jreback]

thanks you sir!