Update c8 configuration

[PyvesB]

• adds a few extra ignored folders and deletes no-longer relevant ones.
• renames .nycrc.json to .c8rc.json, we hadn't done so in switch to c8 for code coverage #6778 as we were still evaluating c8 at the time.
• stops attempting to clean up .nyc_output, we hadn't done so in switch to c8 for code coverage #6778 as we were still evaluating c8 at the time.

[github-actions]

	Warnings
⚠️	This PR modified package.json, but not package-lock.json - Perhaps you need to run npm install?

	Messages
📖	✨ Thanks for your contribution to Shields, @PyvesB!

Generated by 🚫 dangerJS against 5462245

[chris48s]

We could also remove this from gitignore:

shields/.gitignore

Lines 53 to 54 in 848e409

	# nyc test coverage
	.nyc_output

[chris48s]

I've pointed out one more thing we can remove, but it doesn't need another round of review after that. Feel free to just bypass branch protections to merge

[PyvesB]

Yeah, I wasn't sure whether to keep it or not as it was added in bulk with other stuff in 7c4b2b6, but happy to remove it!