[native] Remove CoolOrNerdModeSelection and KeyserverSelection from registration flow

Summary: This diff keeps them in the codebase for now, in case we want to bring this back.

Test Plan: Tested opening the registration flow from the main screen and from FullscreenSIWEPanel. Make sure CoolOrNerdModeSelection and KeyserverSelection don't appear. Make sure that I am able to successfully register

Reviewers: ginsu, inka

Reviewed By: inka

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11972