video_core: Remove unused Renderer enumeration

Currently we only have an OpenGL renderer, so this is unused in code
(and occupies the Renderer identifier in the VideoCore namespace).

src/video_core/video_core.h

@@ -13,8 +13,6 @@ namespace VideoCore {
 
 class RendererBase;
 
-enum class Renderer { Software, OpenGL };
-
 // TODO: Wrap these in a user settings struct along with any other graphics settings (often set from
 // qt ui)
 extern std::atomic<bool> g_toggle_framelimit_enabled;