CLN: remove unused axis keyword from Block.where
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

thanks. any perf changes? (e.g. you added `copy=False`) > thanks. any perf changes? (e.g. you added copy=False)

we save a copy and make a mask more efficiently, but nothing earth-shaking