Remove dill version request

[JunCEEE]

This is tested with dill==0.3.8

[JunCEEE]

@mads-bertelsen Interestingly it fails on the test for McStasScript.

[JunCEEE]

@CFGrote Hi, there is an issue with the newer version of dill>0.3.5.1, for example dill==0.3.8. Do you have any ideas for a solution?

[JunCEEE]

Some hints:
The error from test_GSC_dump.py of SimEx-Lite

TypeError: The object in the file /tmp/pytest-of-juncheng/pytest-13/test_dump_and_load0/dumptest.dump is not a <class 'SimExLite.SourceCalculators.GaussianSourceCalculator.GaussianSourceCalculator'>, but <class 'SimExLite.SourceCalculators.GaussianSourceCalculator.GaussianSourceCalculator'>