[Protos] Remove tunnelbroker.proto

Summary:
Remove legacy tunnelbroker protobuf file and related code.

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

Test Plan: Test gates pass

Reviewers: ashoat, atul, varun, bartek, max

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7479