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/CScriptVisorFlare.hpp

@@ -21,7 +21,7 @@ public:
   void AcceptScriptMsg(EScriptObjectMessage msg, TUniqueId objId, CStateManager& stateMgr) override;
   void PreRender(CStateManager&, const zeus::CFrustum&) override;
   void AddToRenderer(const zeus::CFrustum&, CStateManager&) override;
-  void Render(const CStateManager&) const override;
+  void Render(CStateManager&) override;
 };
 
 } // namespace urde