Cleaning & conventions for Econ module 2 - Post UCB

[nuke-web3]

Part of #710

TODO

• Refactor Econ slides to be markdown #815
• Review README is correct with SMEs
• Confirm lesson plans are all no longer needed with SMEs
• update README with more faculty facing details ala https://github.com/Polkadot-Blockchain-Academy/pba-content/blob/5b5f99d809b4e15348104b7c6e43da6f95a4a1b7/syllabus/1-Cryptography/README.md

[nuke-web3]

FYI waiting on #855 to be resolved before this is merged.

[nuke-web3]

@jonasW3F @AlfonsoCev I am going to merge this as is, so it's easy to view on https://do-not-share-pba-internal.on.fleek.co/

In the source, you only need to look at files in syllabus/2-Economics - all else is external, no assets/... separation anymore.

Note that this PR's OP still has TODO items I hope you can do ASAP to get into the new book - here is the WIP repo for that: https://github.com/Polkadot-Blockchain-Academy/testing-only

I am happy to migrate changes from here to there. We need to get this done yesterday so please to rush. 🙏