packfile: drop sha1_pack_name()

packfile: drop sha1_pack_name()

The sha1_pack_name() function has a few ugly bits:

  - it writes into a static strbuf (and not even a ring buffer of them),
    which can lead to subtle invalidation problems

  - it uses the term "sha1", but it's really using the_hash_algo, which
    could be sha256

There's only one caller of it left. And in fact that caller is better
off using the underlying odb_pack_name() function itself, since it's
just copying the result into its own strbuf anyway.

Converting that caller lets us get rid of this now-obselete function.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>