(imenu--menubar-select): No longer interactive.

(imenu--menubar-select): No longer interactive.
(imenu-create-submenu-name): Function deleted.
(imenu-example--create-lisp-index): Don't use it.
(imenu--generic-function): Don't use imenu-create-submenu-name.
(imenu-submenu-name-format): Variable deleted.
(imenu--split-menu): Use TITLE as the head of the new list.
Don't split if everything fits in one level.
(imenu--split-submenus): New function.
(imenu-update-menubar): Use imenu--split-submenus.
(imenu--mouse-menu): Use imenu--split-submenus.