Fix ODR violation for ShaderModelRendererInternals.
ShaderModelRendererInternals is defined twice, once by ModelRenderer.cpp and once by HWLightingModelRenderer.cpp.
Having two different definitions in the global namespace is a violation of the C++ One-Definition-Rule.
Patch by: StefanBruens
Reviewed By: wraitii, Vladislav
Differential Revision: https://code.wildfiregames.com/D2932