btrfs: qgroup: remove ASYNC_COMMIT mechanism in favor of reserve retry-after-EDQUOT

btrfs: qgroup: remove ASYNC_COMMIT mechanism in favor of reserve retry-after-EDQUOT

commit 4ffe39486610234e1a212f564edfac72a2a844ef upstream

commit 2494bafcd2fd ("btrfs: qgroup: Commit transaction in advance to
reduce early EDQUOT") tries to reduce the early EDQUOT problems by
checking the qgroup free against threshold and tries to wake up commit
kthread to free some space.

The problem of that mechanism is, it can only free qgroup per-trans
metadata space, can't do anything to data, nor prealloc qgroup space.

Now since we have the ability to flush qgroup space, and implemented
retry-after-EDQUOT behavior, such mechanism can be completely replaced.

So this patch will cleanup such mechanism in favor of
retry-after-EDQUOT.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>