Fix use of unversioned provides

As explained in #1766 (closed):

• either have a versioned provides= line
• or have a unversioned provides line with a provider_priority

Add a CI test, and fix it in all packages.

Noteworthy:

• mobile-config-firefox: upgrade to 3.1.0 while at it, there was some minor stuff in master that wasn't in the release and I didn't make one in a while: https://gitlab.com/postmarketOS/mobile-config-firefox/-/tags/3.1.0
• mkbootimg-osm0sis: upgrade to 2021.08.06 while at it
• treewide: remove linux-headers replacements (instead of fixing wrong use of provides there)
• device/community/soc-*-ucm: set provider_priority depends on aports!40814

See commit messages for details.

• Fix #1766 (closed)
• Fix #462 (closed)
• Fix #1171 (closed)