gitlab: remove ability to skip 'ninja dist'
gitlab: remove ability to skip 'ninja dist'

The "DIST=skip" flag as used in CentOS 7 jobs to workaround a problem
with older git versions. This is no longer required since

  commit d35003aee7d057e66d935cfd919ea86d5d450c4c
  Author: Andrea Bolognani <abologna@redhat.com>
  Date:   Tue May 4 10:45:29 2021 +0200

    ci: Drop CentOS 7

Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Signed-off-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,libvirt/libvirt,olafhering/libvirt,jfehlig/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt