CLN/TYP: Removed redundant 'int' from pandas/_typing.py
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

As @simonjayhawkins says [here](https://github.com/pandas-dev/pandas/pull/30403#discussion_r360828949) (comment), having ```Union``` with both ```int``` and ```float``` is redundant.