feat(refactor): don't persist system external accounts, remove proxy delegates state

[rossbulat]

• No longer stores proxy delegates in a separaste state object, and instead introduces a formatProxiesToDelegates to discover them on the fly. This prevents re-renders.
• system external accounts are no longer persisted in local storage.

About system external account changes

To prevent edge cases in read only account management, system accounts are no longer persisted in local storage.

System accounts are discovered after the initial account import process, and may replace existing user based read only accounts. This is a dynamic process, and the user added accounts still need to be persisted in local storage. This update will allow these accounts to be remembered even if they are updated to system accounts.

Includes a migration to remove existing system external accounts from local storage.