Get rid of all the manual purecopy calls in menu-bar definitions.

Get rid of all the manual purecopy calls in menu-bar definitions.
* lisp/loadup.el (purify-flag): Pre-grow the hash-table to reduce the
memory use.
* lisp/bindings.el (bindings--define-key): New function.
* lisp/vc/vc-hooks.el, lisp/replace.el, lisp/menu-bar.el:
* lisp/international/mule-cmds.el, lisp/emacs-lisp/lisp-mode.el:
* lisp/buff-menu.el, lisp/bookmark.el:
* bindings.el: Use it to purecopy define-key bindings.
* src/fns.c (maybe_resize_hash_table): Output message when growing the
purify-hashtable.