Merge branch 'ps/remove-packfile-store-get-packs'

Merge branch 'ps/remove-packfile-store-get-packs'

Two slightly different ways to get at "all the packfiles" in API
has been cleaned up.

* ps/remove-packfile-store-get-packs:
  packfile: rename `packfile_store_get_all_packs()`
  packfile: introduce macro to iterate through packs
  packfile: drop `packfile_store_get_packs()`
  builtin/grep: simplify how we preload packs
  builtin/gc: convert to use `packfile_store_get_all_packs()`
  object-name: convert to use `packfile_store_get_all_packs()`