Changes

Revert "Delete content of Jenkins job cache folders"

This reverts commit ad5a73c519d79d740e808296c1520962749ad167.

That committ was an attempt at improving the Jenkins CI's
reliability, but it has caused issues:
- the command is not OS-agnostic and does not work on at least Windows
- the /.cache folder, despite it's label, contains more than yarn, so removing it altogether is not a good idea. In any case `yarn cache clean` works perfectly, AFAICT. The attempted fix was more to address the 'electron-gyp` folder.

I might come-back with a follow-up, if I can successfully improve CI