[native] Removing Tunnelbroker-related protobuf compiled files

Summary:
This diff remove Tunnelbroker-related protobuf compiled files for gRPC-C++ which was removed and these files are no longer needed.

Linear task: ENG-2276

Test Plan:

1. The iOS app is successfully built.
2. In the XCode project files list there are no files left with the names like %grpc% and %tunnelbroker%.

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5792