[Keyserver/rust-node-addon] Remove tunnelbroker grpc client

Summary:
We are transitioning from grpc based communication to websockets for
bidi communications.

Remove existing grpc code for keyserver to talk to tunnelbroker.

Part of https://linear.app/comm/issue/ENG-3660

Test Plan: Did yarn cleaninstall, then did a iOS register new user.

Reviewers: ashoat, max, bartek

Reviewed By: ashoat

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D7405