khash: drop broken oid_map typedef

khash: drop broken oid_map typedef

Commit 5a8643eff1 (khash: move oid hash table definition, 2019-02-19)
added a khash "oid_map" type to match the existing "oid" type, which is
a simple set (i.e., just keys, no values). But in setting up the
khash_oid_map typedef, it accidentally referred to "kh_oid_t", which is
the set type.

Nobody noticed the breakage because there are not yet any callers; the
type was added just as a match to the existing sha1 types (whose map
type confusingly _is_ called khash_sha1, and it has no matching set
type).

We could easily fix this with s/oid/oid_map/ in the typedef. But let's
take this a step further, and just drop the typedef entirely.  These
typedefs were added by 5a8643eff1 to match the khash_sha1 typedefs. But
the actual khash-derived type names are descriptive enough; this is just
adding an extra layer of indirection. The khash names do not quite
follow our usual style (e.g., they end in "_t"), but since we end up
using other khash names (e.g., khiter_t, kh_get_oid()) anyway, just
typedef-ing the struct name is not really helping much.

And there are already many cases where we use the raw khash type names
anyway (e.g., the "set" variant defined just above us does not have such
a typedef!).

So let's drop this typedef, and the matching oid_pos one (which actually
_does_ have a user, but we can easily convert it).

We'll leave the khash_sha1 typedef around. The ultimate fate of its
callers should be conversion to kh_oid_map_t, so there's no point in
going through the noise of changing the names now.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>