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/World/CScriptGrapplePoint.cpp

@@ -40,7 +40,7 @@ void CScriptGrapplePoint::Think(float, CStateManager&) {
   // Empty
 }
 
-void CScriptGrapplePoint::Render(const CStateManager&) const {
+void CScriptGrapplePoint::Render(CStateManager&) {
   // Empty
 }