nixos/xserver: let X choose the xkb rules

With libinput used for keyboard, base rules produce incorrect keyboard
layouts. We are removing the option as recommended in the XKB configuration
guide [1] to let X server choose the ruleset. It looks like it chooses
evdev rules which seem to work for some reason

[1]: https://www.x.org/releases/X11R7.6/doc/xorg-docs/input/XKB-Config.html#id2521360

nixos/modules/services/x11/xserver.nix

@@ -700,7 +700,6 @@ in
         Section "InputClass"
           Identifier "Keyboard catchall"
           MatchIsKeyboard "on"
-          Option "XkbRules" "base"
           Option "XkbModel" "${cfg.xkbModel}"
           Option "XkbLayout" "${cfg.layout}"
           Option "XkbOptions" "${cfg.xkbOptions}"