Remove ns-handle-* functions that duplicate x-handle-*.

Remove ns-handle-* functions that duplicate x-handle-*.

* lisp/term/ns-win.el (ns-version-string): Remove unused declaration.
(ns-invocation-args): Change to x-invocation-args.
(ns-handle-switch, ns-handle-numeric-switch, ns-handle-iconic)
(ns-handle-name-switch, ns-ignore-2-arg): Remove.
(ns-handle-nxopen, ns-handle-nxopentemp, ns-ignore-1-arg):
Use x-invocation-args instead of ns-invocation-args.
(ns-initialize-window-system, handle-args-function-alist):
Use x-handle-args instead of ns-handle-args.
* lisp/term/common-win.el (x-handle-args): Also handle nextstep arguments.
* lisp/startup.el (command-line-ns-option-alist): Replace
ns-handle-name-switch, ns-handle-switch, ns-handle-numeric-switch,
ns-handle-iconic with the x- equivalents.