Jl/caip multichain/misc cleanup

[jiexi]

Description

Misc cleanup. Removing KnownCaipNamespace is still not possible because @metamask/util does not have a Wallet enum value

Related issues

See: https://github.com/MetaMask/MetaMask-planning/issues/3050

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[adonesky1]

LGTM!

[adonesky1]

It looks like we do this in the mergeScopes function? Can this TODO be removed as well?

[jiexi]

i removed this comment in a separate open PR, but it won't hurt to remove it in this one too, and so we shall 🙏