odb: drop deprecated wrapper functions

odb: drop deprecated wrapper functions

In the Git 2.51 release cycle we've refactored the object database layer
to access objects via `struct object_database` directly. To make the
transition a bit easier we have retained some of the old-style functions
in case those were widely used.

Now that Git 2.51 has been released it's time to clean up though and
drop these old wrappers. Do so and adapt the small number of newly added
users to use the new functions instead.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>