simulators: remove obsolete consensus, graphql, testnet, portal, and clique simulators

[spencer-tb]

Summary

• Remove ethereum/consensus, replaced by ethereum/eels/* consume-rlp
• Remove ethereum/graphql, not consensus critical, limited cross client value
• Remove eth2/testnet, PoW to PoS transition testing, obsolete since the Merge
• Remove eth2/engine transition tests, TTD based scenarios no longer relevant
• Remove portal/*, Portal Network project abandoned
• Remove smoke/clique, Clique PoA deprecated
• Clean up CI triggers, docs, and devp2p portal discv5 entry

Context

https://notes.ethereum.org/@spencer/hive-purge/

[danceratopz]

Thanks @spencer-tb for pushing and implementing this clean-up!

I would have personally preferred:

• To add new doc content as a separate PR (from this otherwise subtractive PR).
• To remove each simulator as a separate commit (or even separate PRs, as the the merge method seems to be fixed at "Squash and merge" for me), just in case we ever needed to (partially) revert the decision.

But if it's deemed ok to yolo, then it's fine for me. It is in line with what we decided 👍 but as-is, I would prefer if @fjl chimed in to approve and merge.