[Native] Prune protobuf logic from CMakeLists.txt

Summary:
Remove the protobuf projects from
native/cpp/CommonCpp/grpc/CMakeLists.txt

Only the grpc client remains

https://linear.app/comm/issue/ENG-1231

Test Plan: CI gates pass

Reviewers: atul, max, karol, abosh

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D5045