* lisp/simple.el: Use set-temporary-overlay-map for universal-argument.

* lisp/simple.el: Use set-temporary-overlay-map for universal-argument.
(universal-argument-map): Don't use default-bindings.
Bind switch-frame explicitly.  Replace universal-argument-minus with
a conditional binding.
(universal-argument-num-events, saved-overriding-map): Remove.
(restore-overriding-map): Remove.
(universal-argument--mode): Rename from save&set-overriding-map,
and rewrite.
(universal-argument, universal-argument-more, negative-argument)
(digit-argument): Adjust accordingly.
(universal-argument-minus): Remove.
(universal-argument-other-key): Remove.