That's a warning, not an error, and it happens before rendering.
To uninstall, you could do one of these:
- delete the alShader DLLs from your system
- If you're using ARNOLD_PLUGIN_PATH to point to the alShaders, remove the alShaders location from the environment variable
In Maya, use Arnold > Utilities > Convert Deprecated Shaders to get rid of alShaders in a scene.
// Stephen Blair
// Arnold Renderer Support