Remove redundant parentheses from if conditions
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @Giftlin! Thanks for submitting the PR.

 - In the file [`pandas/plotting/_timeseries.py`](https://github.com/pandas-dev/pandas/blob/ed9a40fd396c7c6c646e4bb4a5d45f9f4ef59cce/pandas/plotting/_timeseries.py), following are the PEP8 issues :

> [Line 112:13](https://github.com/pandas-dev/pandas/blob/ed9a40fd396c7c6c646e4bb4a5d45f9f4ef59cce/pandas/plotting/_timeseries.py#L112): [E113](https://duckduckgo.com/?q=pep8%20E113) unexpected indentation

