object-file: drop support for writing objects with unknown types

object-file: drop support for writing objects with unknown types

Since "hash-object --literally" no longer supports objects with unknown
types, there are now no callers of write_object_file_literally() and its
helpers. Let's drop them to simplify the code.

In particular, this gets rid of some ugly copy-and-paste code from
write_object_file_literally(), which is a parallel implementation of
write_object_file(). When the split was originally made, the two weren't
that long, but commits like 63a6745a07 (object-file: update the loose
object map when writing loose objects, 2023-10-01) ended up having to
duplicate some tricky code.

This patch drops all of that duplication and should make things less
error-prone going forward.

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