GFS2: remove vestigial al_alloced

This patch removes the vestigial variable al_alloced from
the gfs2_alloc structure. This is another baby step toward
multi-block reservations.

My next planned step is to decouple the quota variables
from the gfs2_alloc structure so we can use a different
method for allocations.

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