Shed some vestigial dev tooling

[Mr0grog]

~⚠️ This is based on #193; that PR should be merged first. ⚠️~

Based on the discussion in #191, this removes a bunch of dev-time tooling that we no longer actually need or use. It also happens to resolve 31 of our vulnerabilities from dependencies (based on the results of npm audit), including 4 that were rated “critical” (there are 21 total left, 2 of which are “critical”).

Removed:

• QUnit (this was only used to verify that we don’t cause problems when used by a package that is tested with QUnit; I replaced it with a simple test of noConflict(), which is what this is really about)
• Saucelabs
• Coveralls.io (if we want to start using Coveralls.io again, we should probably use their official GitHub Action instead)
• Vendored json2.js package (it never seems to have actually been used)
• Removes a redundant step from the test-browser task in Grunt.

There’s still a little more easy-ish cleanup/updates to do based on #191, and I’ll work on that after this PR lands.

[pimterry]

Can you rebase this on top of main? That should drop the duplicated CI commits that are still shown here.

[Mr0grog]

Done!