[lib] Fix legacy register and SIWE

Summary: D11632 broke these by accidentally including a new parameter to the keyserver request, which fails input validation.

Test Plan: Test legacy register, legacy SIWE, and new registration flow (using legacy registration)

Reviewers: will, atul

Reviewed By: will, atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11667