mm, swap: remove setting SWAP_MAP_BAD for discard cluster

Before alloc from a cluster, we will aqcuire cluster's lock and make sure
it is usable by cluster_is_usable(), so there is no need to set
SWAP_MAP_BAD for cluster to be discarded.

Link: https://lkml.kernel.org/r/20250222160850.505274-5-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>