NoGUI: Move DRM display to GL context

We don't use it for Vulkan.

src/duckstation-nogui/drm_host_interface.h

@@ -1,5 +1,4 @@
 #pragma once
-#include "common/drm_display.h"
 #include "nogui_host_interface.h"
 #include <memory>
 #include <vector>
@@ -38,8 +37,6 @@ private:
   void PollEvDevKeyboards();
   void SetImGuiKeyMap();
 
-  std::unique_ptr<DRMDisplay> m_drm_display;
-
   struct EvDevKeyboard
   {
     struct libevdev* obj;