Replace NS code that implemented font panels in a different way

Replace NS code that implemented font panels in a different way

* doc/emacs/macos.texi (Mac / GNUstep Events): Document removal
of `ns-change-font' event.  The font panels are now implemented
normally, via `x-select-font'.

* lisp/term/common-win.el (x-setup-function-keys): Likewise.

* lisp/term/ns-win.el (global-map, ns-popup-font-panel): Remove.
(x-select-font, mouse-set-font, ns-input-font):
(ns-input-fontsize): Remove.
(ns-respond-to-change-font): Delete function.

* src/nsfns.m (Fns_popup_font_panel): Delete function.
(Fx_select_font): New function.
(syms_of_nsfns): Update subrs.
* src/nsterm.h (@interface EmacsView):
* src/nsterm.m (ns_select_1): New function.
(ns_select): Wrap around that instead.
([EmacsView changeFont:]): Exit nested event loop
([EmacsView showFontPanel:]): New function.