btrfs: remove list_empty() check at warn_about_uncommitted_trans()

At warn_about_uncommitted_trans(), there's no need to check if the list
is empty and return, because list_for_each_entry_safe() is safe to call
for an empty list, it simply does nothing. So remove the check.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -4182,9 +4182,6 @@ static void warn_about_uncommitted_trans(struct btrfs_fs_info *fs_info)
 	struct btrfs_transaction *tmp;
 	bool found = false;
 
-	if (list_empty(&fs_info->trans_list))
-		return;
-
 	/*
 	 * This function is only called at the very end of close_ctree(),
 	 * thus no other running transaction, no need to take trans_lock.