CLN: cleanup rank tests
we have rank tests in:

Create a new ``pandas/tests/series/test_rank``
- ``pandas/tests/series/test_analytics``

Create a new ``pandas/tests/frame/test_rank``
- ``pandas/tests/frame/test_analytics``

- ``pandas/tests/test_algos``

Let's remove this and split among the other three
- ``pandas/tests/test_stats`` 

