Use browserslist defaults which is `> 0.5%, last 2 versions, Firefox ESR, not dead`

This allows us to move forward without being held back. Microsoft already replaces the Legacy Edge with the new one on supported Windows versions.

* remove ExplorerMobile since it's included in `dead` browsers
* change Edge to >= 16 otherwise browserslist seems to include >= 17

This is what is currently supported by Microsoft https://en.wikipedia.org/wiki/Microsoft_Edge#Release_history

* Bump supported browsers for v5

- Chrome history: https://en.wikipedia.org/wiki/Google_Chrome_version_history
- Firefox latest ESR (v60): https://www.mozilla.org/en-US/firefox/organizations/
- Edge history: https://en.wikipedia.org/wiki/Microsoft_Edge#Release_history
- Desktop Safari history: https://en.wikipedia.org/wiki/Safari_version_history
- Opera history: https://help.opera.com/en/opera-version-history/

* Update .browserslistrc

* Roll back Chrome several versions for now

Still WIP, but wanting to get this merged, so finding a slightly wider baseline

This reverts commit 5e068eed.