t/helper: stop registering alternates in "ref-store" command

When using the "ref-store" command we support access to multiple
different reference stores. As part of that we allow the caller to
explicitly exercise stores of a submodule. This allows us to verify
low-level behaviour of submodule stores, which is exercised in t1406.

When doing so we also link the submodule's object database into the main
object database. The intent of this is that it allows us to access
objects of the submodule, too. But that functionality is not even
needed anymore: when creating a submodule reference store, we will first
initialize the submodule repository and then initialize the store with
that repository. And as the reference subsystem doesn't depend on
`the_repository` anymore all subsequent object lookups performed by the
reference store will be routed to the submodule repository.

It is thus not needed anymore to register the submodule object store
with the main object database. Remove the call.

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

t/helper/test-ref-store.c

@@ -74,14 +74,6 @@ static const char **get_store(const char **argv, struct ref_store **refs)
 	} else if (!strcmp(argv[0], "main")) {
 		*refs = get_main_ref_store(the_repository);
 	} else if (skip_prefix(argv[0], "submodule:", &gitdir)) {
-		struct strbuf sb = STRBUF_INIT;
-
-		if (!repo_submodule_path_append(the_repository,
-						&sb, gitdir, "objects/"))
-			die("computing submodule path failed");
-		odb_add_to_alternates_memory(the_repository->objects, sb.buf);
-		strbuf_release(&sb);
-
 		*refs = repo_get_submodule_ref_store(the_repository, gitdir);
 	} else if (skip_prefix(argv[0], "worktree:", &gitdir)) {
 		struct worktree **p, **worktrees = get_worktrees(the_repository);