dm: do not set 'discards_supported' in targets that do not need it

The DM target's 'discards_supported' flag is intended to act as an
override.  Meaning, even if the underlying storage doesn't support
discards the DM target will.
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

drivers/md/dm-era-target.c

@@ -1513,7 +1513,6 @@ static int era_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	ti->flush_supported = true;
 
 	ti->num_discard_bios = 1;
-	ti->discards_supported = true;
 	era->callbacks.congested_fn = era_is_congested;
 	dm_table_add_target_callbacks(ti->table, &era->callbacks);
 

drivers/md/dm-raid.c

@@ -2887,9 +2887,6 @@ static void configure_discard_support(struct raid_set *rs)
 	bool raid456;
 	struct dm_target *ti = rs->ti;
 
-	/* Assume discards not supported until after checks below. */
-	ti->discards_supported = false;
-
 	/*
 	 * XXX: RAID level 4,5,6 require zeroing for safety.
 	 */
@@ -2914,9 +2911,6 @@ static void configure_discard_support(struct raid_set *rs)
 		}
 	}
 
-	/* All RAID members properly support discards */
-	ti->discards_supported = true;
-
 	/*
 	 * RAID1 and RAID10 personalities require bio splitting,
 	 * RAID0/4/5/6 don't and process large discard bios properly.