[services] Tunnelbroker - Removing the old API

Summary:
This diff removes the old legacy API methods from the Tunnelbroker API including the proto file and calls from the native codebase.
Old legacy API methods that should be removed:

• CheckIfPrimaryDeviceOnline
• BecomeNewPrimaryDevice
• SendPong

These methods were added prior 0.1 and are not used anymore.

These diff changes take place in:

• The protobuff file and its generated ones - by removing the API calls;
• Native C++ network client-related codebase - by removing the API-related methods;
• Tunnelbroker Rust gRPC server - by removing the empty handlers for the old API.

Linear task: ENG-1334

Test Plan: Services and native iOS and Android builds are successful.

Reviewers: atul, tomek, jon

Reviewed By: atul, tomek

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5596