Refactor PYTHON_PATH out of MATS

[ian-noaa]

Problem

MATS manually sets the PYTHON_PATH for our python-shell dependency. To reduce the amount of code we have and to reduce manual configuration, we'd like to refactor the code so MATS uses whatever python3 resolves to.

Solution

Remove MATS PYTHON_PATH handling. python-shell now by default will use whatever python3 resolves to.

No Go's

Describe any features or behaviors that have been considered and rejected as out of scope for this feature

Additional context

Our containers are already set up to provide an appropriate python3, with dependencies. Local development would work as before. However, there is probably some opportunity to setup a virtualenv for MATS/METexpress so we don't have to use the global Python. This would require more tool wrangling to work with MATS locally so would require some thought.

[github-actions]

This issue is stale because it has been open 90 days with no activity.