Remove more XEmacs compat code from ediff*.el

Remove more XEmacs compat code from ediff*.el

* lisp/vc/ediff-init.el (ediff-H-glyph):
* lisp/vc/ediff-util.el (ediff-inferior-compare-regions)
(ediff-setup-keymap):
* lisp/vc/ediff-wind.el (ediff-control-frame-parameters)
(ediff-prefer-iconified-control-frame)
(ediff-setup-control-frame, ediff-xemacs-select-frame-hook): Remove
XEmacs compat code and declare compatibility functions obsolete.

* lisp/vc/ediff-init.el (ediff-temp-file-prefix): Redefine as
obsolete variable alias for 'temporary-file-directory'.
* lisp/vc/ediff-util.el (ediff-make-temp-file): Don't use obsolete
variable name.