GFS2: Remove old, unused linked list code from quota

This is the kernel portion of the patch-set for upstream gfs2,
to remove the quota-linked-list stuff and replace it with
fiemap-based traversal of the quota file.

The corresponding userland fixes have been pushed to
STABLE3 and master branches of cluster.git and gfs2-utils.git
respectively (Refer Red Hat bug #536902).

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