dm: remove unused _rq_tio_cache and _rq_cache

Also move dm_rq_target_io structure definition from dm-rq.h to dm-rq.c

Fixes: 6a23e05c2f ("dm: remove legacy request-based IO path")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-rq.c

@@ -12,6 +12,22 @@
 
 #define DM_MSG_PREFIX "core-rq"
 
+/*
+ * One of these is allocated per request.
+ */
+struct dm_rq_target_io {
+	struct mapped_device *md;
+	struct dm_target *ti;
+	struct request *orig, *clone;
+	struct kthread_work work;
+	blk_status_t error;
+	union map_info info;
+	struct dm_stats_aux stats_aux;
+	unsigned long duration_jiffies;
+	unsigned n_sectors;
+	unsigned completed;
+};
+
 #define DM_MQ_NR_HW_QUEUES 1
 #define DM_MQ_QUEUE_DEPTH 2048
 static unsigned dm_mq_nr_hw_queues = DM_MQ_NR_HW_QUEUES;