TST: Remove assertEquals
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.

@sinhrks while don't we just make `assertEquals` == `assertEqual` (with a warning) though
 Made suggested changes based on the [unittest doc](https://docs.python.org/3/library/unittest.html#deprecated-aliases). 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.
 thanks you sir!
