UICommon: Avoid including Xrandr.h

Xlib has really terrible headers that declare non-namespaced
macros and typedefs for common words.

Just wasted 10 minutes trying to figure out why a unit test failed
to build before I remembered it was Xrandr.h conflicting with our
enum class members again.

To fix the issue, this removes the Display* parameter from the
EnableScreensaver function (which was unused) so we don't have
to include Xrandr.h anymore.

Source/Core/UICommon/X11Utils.cpp

@@ -43,7 +43,7 @@ bool ToggleFullscreen(Display* dpy, Window win)
   return true;
 }
 
-void InhibitScreensaver(Display* dpy, Window win, bool suspend)
+void InhibitScreensaver(Window win, bool suspend)
 {
   char id[11];
   snprintf(id, sizeof(id), "0x%lx", win);