[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