Kconfig: remove unused function 'menu_get_root_menu'

There is nowhere calling `menu_get_root_menu` function,
so remove it.

Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
index fa8c010..c396aa1 100644
--- a/scripts/kconfig/lkc.h
+++ b/scripts/kconfig/lkc.h
@@ -98,7 +98,6 @@
 bool menu_is_visible(struct menu *menu);
 bool menu_has_prompt(struct menu *menu);
 const char *menu_get_prompt(struct menu *menu);
-struct menu *menu_get_root_menu(struct menu *menu);
 struct menu *menu_get_parent_menu(struct menu *menu);
 bool menu_has_help(struct menu *menu);
 const char *menu_get_help(struct menu *menu);
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 3d6f7cb..62b6313 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -661,11 +661,6 @@
 	return NULL;
 }
 
-struct menu *menu_get_root_menu(struct menu *menu)
-{
-	return &rootmenu;
-}
-
 struct menu *menu_get_parent_menu(struct menu *menu)
 {
 	enum prop_type type;