btrfs: remove redundant clearing of NODISCARD

If no discard mount option is specified, including the NODISCARD option,
we make the async discard the default option then we don't have to call
the clear_opt again to clear the NODISCARD flag. Though this makes no
difference, that the call is redundant has been pointed out several
times so we better remove it.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -3689,7 +3689,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	    fs_info->fs_devices->discardable) {
 		btrfs_set_and_info(fs_info, DISCARD_ASYNC,
 				   "auto enabling async discard");
-		btrfs_clear_opt(fs_info->mount_opt, NODISCARD);
 	}
 
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY