OpenWeatherMap integration cannot be removed

In the log:
The openweathermap platform for the sensor integration does not support platform setup. Please remove it from your config.

I have removed OpenWeatherMap from ‘configuration.yaml’ and from Integrations in the UI. Still I get this message. If I remove the secret used by this integration the core even refuses to start fully.

It seems that HA keeps old stuff around for this, but I have no idea where and how to get rid of it.

Any ideas?