refacto: remove get_gui_env & draw_load_screen from RenderingEngine singleton

src/client/client.h

@@ -347,6 +347,7 @@ class Client : public con::PeerHandler, public InventoryManager, public IGameDef
 	float mediaReceiveProgress();
 
 	void afterContentReceived();
+	void showUpdateProgressTexture(void *args, u32 progress, u32 max_progress);
 
 	float getRTT();
 	float getCurRate();