Drop clone + run of tutorial tests

[Baltoli]

In #3901, we dropped the PL tutorial as a separate step when running tests in CI, and instead opted to upstream a selection of the supported definitions into the K regression test suite.

In #3956, the change to prohibit rather than deprecate macro-like attributes on non-production sentences broke CI because it's still trying to run the full set of PL tutorial tests via the cloned repository.

We should:

• Drop this explicit testing step from the K CI; doing so was the point of moving the tests into the regression test suite in the first place.
• Modernise the PL tutorial definitions and set up CI on that repository: Set up CI pl-tutorial#6