build: update README to indicate that source has moved and delete all files (#893)

Towards https://github.com/googleapis/google-cloud-python/issues/10892.
230 files changed
tree: 4edb6506b2c085225bda8c94ae6db361826d4ade
  1. .repo-metadata.json
  2. LICENSE
  3. README.rst
  4. SECURITY.md