dm: remove request-based DM queue's lld_busy_fn hook

DM multipath is the only caller of blk_lld_busy() -- which calls a
queue's lld_busy_fn hook.  Request-based DM doesn't support stacking
multipath devices so there is no reason to register the lld_busy_fn hook
on a multipath device's queue using blk_queue_lld_busy().

As such, remove functions dm_lld_busy and dm_table_any_busy_target.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.h

@@ -70,7 +70,6 @@ void dm_table_presuspend_undo_targets(struct dm_table *t);
 void dm_table_postsuspend_targets(struct dm_table *t);
 int dm_table_resume_targets(struct dm_table *t);
 int dm_table_any_congested(struct dm_table *t, int bdi_bits);
-int dm_table_any_busy_target(struct dm_table *t);
 unsigned dm_table_get_type(struct dm_table *t);
 struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
 bool dm_table_request_based(struct dm_table *t);