[tunnelbroker] Remove lazy_static dependency

Summary:
Follow up ENG-2900.
This was a dead dependency - it's unused in tunnelbroker.

Test Plan: cd services/tunnelbroker && cargo build

Reviewers: jon, varun

Reviewed By: jon, varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8703