* lisp/emacs-lisp/eieio: A bit more cleanup, removing compat code.

* lisp/emacs-lisp/eieio-core.el (eieio-compiled-function-arglist): Remove.
(eieio--with-scoped-class): Use `declare'.
(eieio-defclass): Remove compatibility code.
(no-method-definition, no-next-method, inconsistent-class-hierarchy)
(invalid-slot-type, unbound-slot, invalid-slot-name): Use define-error.
* lisp/emacs-lisp/eieio-opt.el (eieio-lambda-arglist): Remove.
Use help-function-arglist instead.