dm raid: remove unnecessary discard limits for raid10

BugLink: https://bugs.launchpad.net/bugs/1896578

Commit bcc90d2 ("md/raid10: improve raid10 discard request")
removes raid10's inability to properly handle large discards.  So
eliminate associated constraint from dm-raid's raid10 support.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
(cherry picked from commit f0e90b6)
Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>

drivers/md/dm-raid.c

@@ -3742,17 +3742,6 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	blk_limits_io_min(limits, chunk_size_bytes);
 	blk_limits_io_opt(limits, chunk_size_bytes * mddev_data_stripes(rs));
-
-	/*
-	 * RAID10 personality requires bio splitting,
-	 * RAID0/1/4/5/6 don't and process large discard bios properly.
-	 */
-	if (rs_is_raid10(rs)) {
-		limits->discard_granularity = max(chunk_size_bytes,
-						  limits->discard_granularity);
-		limits->max_discard_sectors = min_not_zero(rs->md.chunk_sectors,
-							   limits->max_discard_sectors);
-	}
 }
 
 static void raid_postsuspend(struct dm_target *ti)