submodule: remove gitmodules_config

Now that the submodule-config subsystem can lazily read the gitmodules
file we no longer need to explicitly pre-read the gitmodules by calling
'gitmodules_config()' so let's remove it.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-submodule-config.c

@@ -32,7 +32,6 @@ int cmd_main(int argc, const char **argv)
 		die_usage(argc, argv, "Wrong number of arguments.");
 
 	setup_git_directory();
-	gitmodules_config();
 
 	while (*arg) {
 		struct object_id commit_oid;