blk-wbt: kill check for legacy queue type

Everything is blk-mq at this point, so it doesn't make any sense
to have this option available as it does nothing.
Reviewed-by: NHannes Reinecke <hare@suse.com>
Tested-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/Kconfig

@@ -155,12 +155,6 @@ config BLK_CGROUP_IOLATENCY
 
 	Note, this is an experimental interface and could be changed someday.
 
-config BLK_WBT_SQ
-	bool "Single queue writeback throttling"
-	depends on BLK_WBT
-	---help---
-	Enable writeback throttling by default on legacy single queue devices
-
 config BLK_WBT_MQ
 	bool "Multiqueue writeback throttling"
 	default y

block/blk-wbt.c

@@ -709,8 +709,7 @@ void wbt_enable_default(struct request_queue *q)
 	if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
 		return;
 
-	if ((q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ)) ||
-	    (q->request_fn && IS_ENABLED(CONFIG_BLK_WBT_SQ)))
+	if (q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ))
 		wbt_init(q);
 }
 EXPORT_SYMBOL_GPL(wbt_enable_default);