(imenu-generic-lisp-expression)

(imenu-generic-lisp-expression)
(imenu-generic-c++-expression, imenu-generic-c-expression)
(imenu-generic-ada-expression, imenu-generic-texinfo-expression)
(imenu-generic-latex-expression): Vars deleted; now handled by the
major modes themselves.
(imenu--scanning-method-alist): Var deleted.
(imenu-default-create-index-function): Don't use that alist.