Codechange: Deduplicate ResolveReal() for resolvers that don't use real sprite groups.

This may change behaviour when multiple loading/loaded stages are provided, as the various copies checked in different orders, however only one result is expected in these cases anyway.

src/newgrf_railtype.cpp

@@ -58,13 +58,6 @@
 	return UINT_MAX;
 }
 
-/* virtual */ const SpriteGroup *RailTypeResolverObject::ResolveReal(const RealSpriteGroup *group) const
-{
-	if (!group->loading.empty()) return group->loading[0];
-	if (!group->loaded.empty())  return group->loaded[0];
-	return nullptr;
-}
-
 GrfSpecFeature RailTypeResolverObject::GetFeature() const
 {
 	return GSF_RAILTYPES;