Remove the MicroBadger badge from 'README.md'. 4.0

[supahgreg]

MicroBadger has been down since July 1st, 2021.

https://web.archive.org/web/20210409135814/https://microbadger.com/shutdown https://github.com/microscaling/microbadger/issues/75

Notes for Reviewers

• [ ] The commit history must be preserved - please use the rebase-merge or standard merge option instead of squash-merge
• [ ] Sync up with the author before merging