Done Criteria

• mplex code and references are removed from Kubo. This includes updating any Kubo docs as well.
• changelog entry with clear removal message
• (TBD) discuss.ipfs.tech post

When this is done, a user will not have the option of enabling mplex in Kubo.

Why Important

TODO: link to the canonical libp2p issue/doc that describes the woes of mplex.

Notes

1. This finishes what was started with turn mplex off by default #9958, where we disabled mplex by default.
2. mplex code that was copied into Kubo for chore: update boxo, go-libp2p, and internalize mplex #10095 should be removed
3. We should do a find/replace in the Kubo repo and ipfs/docs
4. This is currently targeted for Kubo 0.24
5. If you still need mplex, please share your usecase here.