This issues derives from #598.

As part of the discussion of how to structure the specification of the p2p layer, it has been decided to move the existing content to a spec/p2p/legacy-docs/ sub-directory, which now contains the following content:

1. messages/: documents the channel IDs and the message types adopted by the six standard reactors (block and state sync, consensus, evidence, mempool, and PEX), produced in 2021 (spec: remove reactor section tendermint/spec#242).
   • The content needs to be reviewed, in some cases updated (e.g., PEX messages from the retracted v0.35 release)
   • It is not clear whether this documentation should stay here or be on each reactor's documentation/spec.
2. config.md, connection.md, node.md, peer.md: original documentation with a short summary of main components of the p2p layer, produced 2019 (Add Section for P2P tendermint/spec#53) and referred to in the p2p package's README.
   • A relevant portion of this documentation is already present in the newly produced spec/documentation of the p2p layer
   • The content that is only documented here (e.g., Authenticated Encryption Handshake) should be verified, possibly updated, and moved to a new location.

Definition of Done

• The relevant content on these files should be moved to the stable/main documentation.
• These files should either be removed or reference the location of the updated version of its content.