docs: remove shutdown G+ API reference (#1751)
docs: remove shutdown G+ API reference (#1751)

* docs: remove shutdown G+ API reference

* Update README.md

Co-Authored-By: John Pedrie <a51dda7c7ff50b61eaea0444371f4a6a9301e501@pedrie.com>

eRadical/google-api-php-client,michabbb-backup/google-api-php-client,bshaffer/google-api-php-client,googleapis/google-api-php-client,michabbb-backup/google-api-php-client