[tunnelbroker] remove unused dependencies

Summary: @bartek's diff to remove lazy_static brought my attention to the fact that we have a bunch of unused dependencies in the tunnelbroker Cargo.toml.

Test Plan: ran cargo build

Reviewers: jon, bartek

Reviewed By: jon, bartek

Subscribers: ashoat, tomek, bartek

Differential Revision: https://phab.comm.dev/D8731