For the time being, "make all" needs to be run before "make dist" can
succeed as parts of the documentation are generated by programs compiled
during the regular build process.

As only one source tarball is published for each BIND release, make sure
the tarball creation job in GitLab CI only contains one tarball in the
desired format among its artifacts.

Drop the TARBALL_COMPRESSOR .gitlab-ci.yml variable as it is no longer
used in the source tarball creation process.