@bhouston @WestLangley feel free to move this to a better place.

remove unused code (clear coat), oren-nayar, and make envmap work in world space properly while using local space coords.

fix reflectivity (it should modulate specularColor globally), fix GGX Render Equation, clean up BRDF_GGX_Environment to have incident and reflected light, pull out SpecularLightProbe.