Bug 820686 - Remove code after MOZ_CRASH or MOZ_ASSUME_NOT_REACHED. r=(see below)

r=tbsaunde for accessible
r=jmuizelaar for gfx
r=waldo for js
r=roc for layout
r=glandium for mozglue
r=jduell for netwerk
r=khuey for everything else

gfx/layers/opengl/GLManager.cpp

@@ -79,7 +79,6 @@ GLManager::CreateGLManager(LayerManager* aManager)
   }
 
   MOZ_CRASH("Cannot create GLManager for non-GL layer manager");
-  return nullptr;
 }
 
 }