xfs: kill the unused XFS_QMOPT_* flush flags V2

dquots are never flushed asynchronously. Remove the flag and the
async write support from the flush function. Make the default flush
a delwri flush to make the inode flush code, which leaves the
XFS_QMOPT_SYNC the only flag remaining.  Convert that to use
SYNC_WAIT instead, just like the inode flush code.

V2:
- just pass flush flags straight through

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

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

diff --cc fs/xfs/quota/xfs_dquot_item.c
Simple merge

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

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