[Tunnelbroker] Remove C++ codebase
Summary:
Thought that the old codebase would be more useful
when developing the "new" tunnelbroker. However, protocol
and assumption differences between the two made this
legacy codebase less valuable.
Test Plan: N/A
Reviewers: ashoat, varun, bartek
Reviewed By: bartek
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D8212