xfs: remove the per-filesystem list of dquots

Instead of keeping a separate per-filesystem list of dquots we can walk
the radix tree for the two places where we need to iterate all quota
structures.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --cc fs/xfs/xfs_dquot.c
Simple merge

diff --cc fs/xfs/xfs_dquot.h
Simple merge

diff --cc fs/xfs/xfs_qm.c
Simple merge

diff --cc fs/xfs/xfs_qm.h
Simple merge

diff --cc fs/xfs/xfs_qm_syscalls.c
Simple merge