Module config page linked on Management Toolbar
It is because you have added a MENU_NORMAL_ITEM under the admin menu, so it will automatically put it in the admin toolbar (that is also the default so if you exclude that parameter it will also be a menu normal item).

If you change it to MENU_CALLBACK, that will create the link between that url and your page callback, but it will not create an item in the menu.

See hook_menu() for all the menu item types.