Use internal cuts in tests with predictions
Created by: scarlehoff
As per #1347 (closed) and #1141 (closed), since we need cuts when using the python predictions the tests should use internal cuts as well. This PR just changes that part so that the future PR with the libNNPDF predictions to python predictions don't need to change the tests (I already played a bit with it and some regression tests that are asking for a tad too much precision will need to be updated but nothing dramatic).