CActor: Make Render() a non-const function

A few implementations of Render() contain const-casts nested within its
their call hierarchy to get around the fact that this function is marked
const. We can just make the member function non-const to allow removal
of these casts in follow up changes.

Runtime/Camera/CInterpolationCamera.cpp

@@ -27,7 +27,7 @@ void CInterpolationCamera::ProcessInput(const CFinalInput& input, CStateManager&
   // Empty
 }
 
-void CInterpolationCamera::Render(const CStateManager& mgr) const {
+void CInterpolationCamera::Render(CStateManager& mgr) {
   // Empty
 }