Remove the Coq checker (closes GH-1692)

[cpitclaudel]

This checker doesn't read options from _CoqProject, and it's much too slow to be generally useful (and all Emacs Coq users use PG)

[cpitclaudel]

Let's make one last release with Coq and then merge this

[LukeXuan]

Some strange configuration leads me to this pull request, maybe it's time to finally merge it :)

[jcs090218]

No objection to this.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ cpitclaudel
❌ bbatsov
_{You have signed the CLA already but the status is still pending? Let us recheck it.}