btrfs: remove redundant refcount check in btrfs_put_transaction()

Eric Dumazet removed the redundant refcount check for sk_refcnt, I
noticed a similar issue in btrfs_put_transaction().
refcount_dec_and_test() already checks for a zero refcount and
complains, making the preceding WARN_ON redundant. This is a leftover
from the atomic_t times.

Signed-off-by: Xuanqiang Luo <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/transaction.c

···
 
 void btrfs_put_transaction(struct btrfs_transaction *transaction)
 {
-	WARN_ON(refcount_read(&transaction->use_count) == 0);
 	if (refcount_dec_and_test(&transaction->use_count)) {
 		BUG_ON(!list_empty(&transaction->list));
 		WARN_ON(!xa_empty(&transaction->delayed_refs.head_refs));