[TODO by Julien] Check MATH_ENV key obsolescence

[jucor]

To help with the colossal #2253 by @ballPointPenguin , making here a note for myself to:

1. Figure out where the MATH_ENV key is used in the JSON blobs, as per old documentation:
   

   polis/math/doc/configuration.md

   Lines 13 to 18 in a0ced96

   	* **`MATH_ENV`**: This defaults to `dev`, for local development environments.
   	Traditionally we've set this to `prod` and `preprod` for our production and pre-production deployments specifically.
   	This value is used in keying the math export json blobs as found in the `math_main` and other tables in the database.
   	This makes it possible to run multiple math environments (dev, testing, prod, preprod) all on the same database of votes.
   	This setting is something of a relic from an old architecture where prod and preprod environments ran off of the same database, and with the docker infrastructure is generally no longer needed.
   	Nevertheless, when you start the math server, you will need to run it with the same **`MATH_ENV`** setting as you ran the math worker with.

2. Check the distribution of MATH_ENV keys (prod/preprod/dev/test, as flagged by @ballPointPenguin ) in the prodclone database.
3. Confirm that all recent prod convos have the correct MATH_ENV to prod. If not, figure out why by getting historical context from @colinmegill .
4. Check that MATH_ENV is not used anymore in the Python port (🤞 )
5. From that, help confirm that we can fully-one that legacy MATH_ENV complexity.