test/helpers: Replace deprecated recursive rmdir

[taratatach]

Recursive fs.rmdir calls have been deprecated in favor of recursive calls to fs.rm and the deprecation warning is seen as an error by AppVeyor thus failing the scenarios job.

Replacing these calls should get us a green CI again.

Please make sure the following boxes are checked:

• [x] PR is not too big
• [x] it improves UX & DX in some way
• [ ] it includes unit tests matching the implementation changes
• [ ] it includes scenarios matching a new behaviour or has been manually tested
• [x] it includes relevant documentation