submodule: avoid auto-discovery in new working tree manipulator code

All commands that are run in a submodule, are run in a correct setup,
there is no need to prepare the environment without setting the GIT_DIR
variable. By setting the GIT_DIR variable we fix issues as discussed in
10f5c526 (submodule: avoid auto-discovery in
prepare_submodule_repo_env(), 2016-09-01)
Signed-off-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

submodule.c

@@ -1363,7 +1363,7 @@ static int submodule_has_dirty_index(const struct submodule *sub)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
 
-	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+	prepare_submodule_repo_env(&cp.env_array);
 
 	cp.git_cmd = 1;
 	argv_array_pushl(&cp.args, "diff-index", "--quiet",
@@ -1380,7 +1380,7 @@ static int submodule_has_dirty_index(const struct submodule *sub)
 static void submodule_reset_index(const char *path)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
-	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+	prepare_submodule_repo_env(&cp.env_array);
 
 	cp.git_cmd = 1;
 	cp.no_stdin = 1;
@@ -1438,7 +1438,7 @@ int submodule_move_head(const char *path,
 		}
 	}
 
-	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+	prepare_submodule_repo_env(&cp.env_array);
 
 	cp.git_cmd = 1;
 	cp.no_stdin = 1;