Converted windows / 32bit skips into decorators
- [X] xref #18190 
- [ ] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Don't have a 32bit or Windows platform at my disposal so plan to leverage AppVeyor and compare before / after of skips to ensure consistency. If you have other ideas on how to tackle let me know.

FWIW the functions that were previously defined in ``pandas.util.testing`` were scarcely used, but I noticed that a lot of tests manually checked for 32 bit or windows and skipped directly. For consistency, I've updated those to use the decorators as well (will need to go back and do the same thing for matplotlib)