TST/REF: Delete duplicate hist tests
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

The tests deleted in this pr are also found starting here: https://github.com/pandas-dev/pandas/blob/e4f425dddda6b299fe5f5e05f18f128302f8604c/pandas/tests/plotting/test_hist_method.py#L26-L27
