CLN: Removing commented code at pandas/_libs/parsers.pyx
Did as @jbrockmendel suggeted [here](https://github.com/pandas-dev/pandas/pull/29554#discussion_r344942442)

- [x] tests passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
thanks