[services] Tunnelbroker - remove include iostream

Summary:
Depends on D4591

Removing #include <iostream> everywhere. This include was used for std::cout and since we quit using it, we can clear out all such includes.

Test Plan: Tunnelbroker builds.

Reviewers: tomek, max

Reviewed By: tomek, max

Subscribers: ashoat, tomek, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4592