Move `defvar`s used to silence warnings outside of eval-when-compile.
Make sure they don't actually give a value to the var.
* pg-init.el: Simplify.
Use (if t ...) to avoid running `require` at compile-time.
Don't add subdirs to load-path here since this code is never used.
(pg-init--script-full-path, pg-init--pg-root):
Inline their definition into their sole user.
* generic/proof-utils.el (proof-resize-window-tofit):
Inline definitions of window-leftmost-p and window-rightmost-p previously
in proof-compat.el.
* lib/proof-compat.el (proof-running-on-win32): Remove, not used.
(mac-key-mode): Remove, there's no carbon-emacs-package-version in
Emacs≥24.3.
(pg-custom-undeclare-variable): Use dolist.
(save-selected-frame): Remove, save-selected-window also saves&restores
the selected frame at the same time. Update all users (which already
used save-selected-window around it).
(window-leftmost-p, window-rightmost-p, window-bottom-p)
(find-coding-system): Remove, unused.
* hol-light/hol-light.el (caml-font-lock-keywords): Don't try to defvar
it to a dummy value and...
(hol-light): ...check its existence before using it instead.
* coq/coq.el (coq-may-use-prettify): Simplify initialization.