Cannot remove Spoor's required files from published course

[tomgreenfield]

Expected Behaviour

You should be able to remove Spoor completely.

Actual Behaviour

If you have published a course with the Spoor extension at any point, its required files are always included in subsequent publishes.

Steps to Reproduce

1. Add the Spoor extension to a course
2. Publish
3. Remove Spoor
4. Publish
5. Observe that Spoor's required files such as imsmanifest.xml remain in the publish

[moloko]

this isn't confined to spoor; any plugin that uses the 'required' folder to add files to the build (e.g. adapt-contrib-media) will have the same problem

I don't believe there's anything in place in the build process to 'clean' the build of files that have been removed from src

Same issue occurs if using the framework and CLI