automl: tables code sample clean-up [(#3571)](GoogleCloudPlatform/python-docs-samples#3571)

* delete unused tables_dataset samples

* delete args code associated with unused automl_tables samples

* delete tests associated with unused automl_tables samples

* restore get_dataset method/yargs without region tagging

* Restore update_dataset methodsa without region tagging

Co-authored-by: Takashi Matsuo <tmatsuo@google.com>
Co-authored-by: Leah E. Cole <6719667+leahecole@users.noreply.github.com>

Author: 3 people