Object database transactions can be explicitly flushed via
flush_odb_transaction() without actually completing the transaction.
This makes the provided transactional interface a bit awkward. Now that
there are no longer any flush_odb_transaction() call sites, drop the
function to simplify the interface and further ensure that a transaction
is only finalized when end_odb_transaction() is invoked.
Signed-off-by: Justin Tobler <jltobler@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>