CLN: Remove redundant index test from tests/base/test_ops.py
part of #23877
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Boolean indexing is already thoroughly tested in `test_series_mask_boolean` in `tests/indexes/test_na_indexing.py` - [see here](https://github.com/pandas-dev/pandas/blob/master/pandas/tests/indexing/test_na_indexing.py#L7-L61)