Deleting files that are not on GitHub to make GoB a mirror of GitHub.

This makes migrating changes between GitHub and GoB easier.

The copybara script is being moved to Piper, and nobody is actually
using the other script.

Change-Id: I876e0ff90995e7d49fa97d57b86aee5d2e66b14a
ORIGINAL_AUTHOR=Thai Duong <thaidn@google.com>
GitOrigin-RevId: e8463a41307fa0e81a8334cad4708dcc5316ed80