Revert "gfs2: Replace gl_revokes with a GLF flag"

Commit 73118ca8 introduced a glock reference counting bug in
gfs2_trans_remove_revoke.  Given that, replacing gl_revokes with a GLF flag is
no longer useful, so revert that commit.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>