btrfs: rip the first_ticket_bytes logic from fail_all_tickets

This was a trick implemented to handle the case where we had a giant
reservation in front of a bunch of little reservations in the ticket
queue.  If the giant reservation was too large for the transaction
commit to make a difference we'd ENOSPC everybody out instead of
committing the transaction.  This logic was put in to force us to go
back and re-try the transaction commit logic to see if we could make
progress.

Instead now we know we've committed the transaction, so any space that
would have been recovered is now available, and would be caught by the
btrfs_try_granting_tickets() in this loop, so we no longer need this
code and can simply delete it.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>