Drop fixed pipeline support code (#15421)

OpenGL 2.0 is now mandatory.

src/client/mesh_generator_thread.h

@@ -70,11 +70,9 @@ private:
 	std::mutex m_mutex;
 
 	// TODO: Add callback to update these when g_settings changes
-	bool m_cache_enable_shaders;
 	bool m_cache_smooth_lighting;
 
 	void fillDataFromMapBlocks(QueuedMeshUpdate *q);
-	void cleanupCache();
 };
 
 struct MeshUpdateResult