builtin/repack.c: avoid using `hash_to_hex()` in pack geometry
In previous commits, we started passing either repository or git_hash_algo pointers around to various spots within builtin/repack.c to reduce our dependency on the_repository in the hope of undef'ing USE_THE_REPOSITORY_VARIABLE. This commit takes us as far as we can (easily) go in that direction by removing the only use of a convenience function that only exists when USE_THE_REPOSITORY_VARIABLE is defined. Unfortunately, the only other such function is "is_bare_repository()", which is less than straightforward to convert into, say, "repo_is_bare()", the latter of the two accepting a repository pointer. Punt on that for now, and declare this commit as the stopping point for our efforts in the direction of undef'ing USE_THE_REPOSITORY_VARIABLE. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>