fix(wpcarro/clipmenu): Enable services.clipmenu

Restore `clipmenu.el` functionality!

After running `sudo rebuild-system` I still needed to
`systemctl --user start clipmenu`, which I didn't expect. Maybe this will DWIM
after a reboot.

Change-Id: I51550561c5b6d253cd52790749d07a2e3e72aecc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6024
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

users/wpcarro/common.nix

@@ -26,6 +26,9 @@ in
   };
 
   services = {
+    # Remodel the system clipboard as a list instead of a point.
+    clipmenu.enable = true;
+
     locate.enable = true;
 
     depot.automatic-gc = {

users/wpcarro/emacs/default.nix

@@ -12,7 +12,6 @@ let
   emacsBinPath = makeBinPath (
     wpcarro.common.shell-utils ++
     (with pkgs; [
-      clipmenu
       ispell
       nix
       pass
@@ -55,8 +54,6 @@ let
       vterm
       base16-theme
       password-store
-      # TODO(wpcarro): Prefer an Emacs client for clipmenud.
-      clipmon
       csharp-mode
       dockerfile-mode
       evil