[lib] Don't clear authoritative keyserver cookie during identity auth

Summary: IDENTITY_REGISTER_SUCCESS and IDENTITY_LOG_IN_SUCCESS currently result in the authoritative keyserver's cookie being cleared (anonymous cookie replaced with null), which results in a bunch of rerenders. It's one of the factors contributing to ENG-7385, since it results in the very first keyserverAuth attempt (triggered by SET_ACCESS_TOKEN) being cancelled almost immediately (by IDENTITY_REGISTER_SUCCESS).

Test Plan: I added some utils that track why a memo is being re-run, and was able to confirm that the cookie was no longer causing memos to re-run

Reviewers: inka

Reviewed By: inka

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11654