[GFS2] Introduce gfs2_remove_from_ail

This collects together the operations required to remove a gfs2_bufdata
from the ail lists. Its only called from two places to start with, but
expect to see more of this function in future.

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

diff --cc fs/gfs2/glops.c
Simple merge

diff --cc fs/gfs2/log.c
Simple merge

diff --cc fs/gfs2/log.h
Simple merge