Consider retiring the Zebra RFC process

[teor2345]

Motivation

Some external developers have asked us if they should write Zebra RFCs. But the Zebra team itself hasn't written a RFC for 2 years.

This is because:

• RFCs were a lot of work to create, because they need a PR approval for every minor change
• A point-in-time RFC quickly becomes outdated

Instead, we have been using these docs for these reasons:

• A notion pad, google doc, HackMD, or google diagram is easier to draft and collaboratively edit
• It's easier to keep Rust module documentation up to date, because it's closer to the code
• If we need extra documentation, we just put a living document directly in the dev (or user) docs in the book

Since the unused and outdated RFC process can be confusing, let's decide if we want to retire it?
If we do, let's document how we want developers to do requirements/designs in a living dev book doc?

Specifications

If we retire RFCs, the template, RFC section page, and the links to the RFC section should be updated:
https://github.com/ZcashFoundation/zebra/blob/main/book/src/dev/rfcs/0000-template.md

Complex Code or Requirements

No response

Testing

No response

Related Work

No response