BUG: Fix to_excel writers handling of cols
- [x] closes #31677
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry - pending https://github.com/pandas-dev/pandas/pull/31723

Ref: https://github.com/pandas-dev/pandas/pull/31723

cc. @WillAyd @jbrockmendel 
Hello @alimcmaster1! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-02-06 21:26:42 UTC lgtm Can you add a whatsnew for 1.0.2? thanks @alimcmaster1 