Re: [PATCH 14/16] packfile: remove `get_packed_git()`

> We have two different functions to retrieve packfiles for a packfile
> store:
>
>   - `get_packed_git()` returns the list of packfiles directly.
>
>   - `get_all_packs()` does more work and also prepares packfiles that
>     are being indexed by a multi-pack-index.
>

> The distinction is not immediately obvious. Furthermore, to make the
> situation even worse, `get_packed_git()` would return the same result as
> `get_all_packs()` once the latter has been called once as they both
> refer to the same list.
>
> As it turns out, the distinction isn't necessary. We only have a couple
> of callers of `get_packed_git()`, and all of those callers are prepared
> to call `get_all_packs()` instead:
>
>   - "builtin/gc.c": We explicitly check how many packfiles aren't
>     contained in the multi-pack-index, so loading extra packfiles that
>     are indexed by it won't change the result.
>
>   - "builtin/grep.c": We only care `get_packed_git()` to prepare eagerly
>     load packfiles. In the preceding commit we have started to expose

>     `packfile_store_prepare()`, which is a more direct way of achieving
>     the same result.
>
>   - "object-name.c": `find_abbrev_len_for_pack()` and `unique_in_pack()`
>     exit early in case the multi-pack index is set, so both callsites of
>     `get_packed_git()` know to handle packs loaded via the MIDX already.
>
> Convert all of these sites to use `get_all_packs()` instead and remove
> `get_packed_git()`.
>