Summary:
IMAP no longer appears on the onboarding account list, and the option to
edit connection settings does not appear for any of the visible account
types. Custom IMAP accounts can still be added via a menu option.
Fixes T7474
Test Plan: tested locally
Reviewers: juan, jackie, evan
Reviewed By: evan
Maniphest Tasks: T7474
Differential Revision: https://phab.nylas.com/D3636