[GFS2] Remove all_list from lock_dlm

I discovered that we had a list onto which every lock_dlm
lock was being put. Its only function was to discover whether
we'd got any locks left after umount. Since there was already
a counter for that purpose as well, I removed the list. The
saving is sizeof(struct list_head) per glock - well worth
having.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>