[CDRIVER-4640] Remove the Release Archive (#1333)

* Remove CMake code for source distribution

This removes code that accumulates lists of sources to include in the
source dist, as well as the targets which generate it.

* "RELEASE" mode does not use release archive
* link-sample tasks do not use the source archive
* No more make-release-archive
* Rename make_release_archive -> make_docs
* Rename the variant
* Define a variant tag for protecting merges
* Use stable Fedora for RPM build (for now)
* Use git archive to create the source archive
* Bring packaging tasks as PR-protected
* Tweak pkg version detection
* Tweak spec patchfile
* Get source filename from rpmspec
* Note pending removal of the release archive