After commits 004ea62 and 092dd65, Emacs can find packages in a system
profile, so it autoloads guix code without additional hacks, which can
be removed now.
* gnu/system.scm (emacs-site-file, emacs-site-directory): Remove.
(operating-system-etc-service): Adjust accordingly.
(operating-system-environment-variables): Remove EMACSLOADPATH.