btrfs: remove unused set/clear_pending_info helpers

The last users of these helpers were removed in 5297199a ("btrfs:
remove inode number cache feature") so delete these helpers.

The point was for mount options that were applicable after transaction
commit so they could not be applied immediately. We don't have such
options anymore and if we do the patch can be reverted.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>