`generate_cylc_workflow.py` and `testreporter.py` should be renamed to remove `.py` extension

For the most part, executable scripts in cime do not have any extension. This makes sense to me: when you're running a script, it shouldn't matter what language that script is written in - and the command to run the script ideally shouldn't change if the script's language changes in the future.

But I noticed two exceptions: `generate_cylc_workflow.py` and `testreporter.py`. I feel that these should be renamed to remove the `.py` extension.