Clean-up CI files

[zm711]

With #1627, we piloted not using caching anymore. Especially with the speed of creating these envs now (currently the slowest step is installing wine, which takes ~ 1min). If we are fine with not caching our conda env after a maintenance cycle then it might be worth doing the following:

Remove environment_testing.yml--> this file only has datalad and pip with the conda-forge channel in it. Only nice for updating a cache which we no longer have.

Clean up the io-testing.yml where currently I've only commented out the cache code. I think it looks messy so maybe we want to delete the commented out code ?