Follow-up polishing work for the tendermint/IBC unforking

[erwanor]

This is an issue tracking small scale improvements and miscellaneous polishing that we should do as follow-ups to the unforking (#1650)

• Remove obsolete comments (rg TODO(erwan))
• Make clippy happy
• Remove stub verification methods in the IBC module (penumbra_component::ibc::connection)
• stop pinning ics23 versions
• TBD

[conorsch]

Discussed this at IBC sync. Most of the work tracked in this ticket was achieved in 2022Q4. There are still a few lingering TODOs, but those are best handled as part of dedicated assurance work, shortly to come. This ticket wasn't tracked as part of #454, so we're closing it out, and will continue to use #454 as the One IBC Ticket to Rule Them All.