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 <[email protected]>
Co-authored-by: Leah E. Cole <[email protected]>

Author: 3 people