Remove jenkins tests

[anton-seaice]

I suggest we remove the current tests (jenkins and test folder), as they will at some point be replaced by #315 or similar. The server they ran on has been shut-down.

EDIT: As an interim, I suggest we keep the test folder and provide a script so it can be triggered manually as a job in the gadi queue

[navidcy]

Why don't we remove them when the GitHub Actions change of #315 is implemented? Why we need to remove them beforehand? Is not that clear to me. Is there a reason @anton-seaice?

(Are the Jenkins tests actually working atm?)

[anton-seaice]

Mostly this annoys me on the github landing page:

[anton-seaice]

Closed by #340