object-store: drop `loose_object_path()`

object-store: drop `loose_object_path()`

The function `loose_object_path()` is a trivial wrapper around
`odb_loose_path()`, with the only exception that it always uses the
primary object database of the given repository. This doesn't really add
a ton of value though, so let's drop the function and inline it at every
callsite.

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