repository: stop reading loose object map twice on repo init

repository: stop reading loose object map twice on repo init

When initializing a repository via `repo_init()` we end up reading the
loose object map twice:

  - `apply_repository_format()` calls `repo_set_compat_hash_algo()`,
    which in turn calls `repo_read_loose_object_map()` if we have a
    compatibility hash configured.

  - `repo_init()` calls `repo_read_loose_object_map()` directly a second
    time.

Drop the second read of the loose object map in `repo_init()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>