vertex-ai-samples refactor(egen): template fixes, adds clean up steps

This PR consists of the following updates:

1. Refactors the notebook according to the notebook template (removes boilerplate elements, renames REGION with LOCATION and re-structures the sections).
2. Removes the usage of future tense(will) according to the guidelines.
3. Adds model deletion steps in clean up section.

REQUIRED: Fill out the below checklists or remove if irrelevant

If you are opening a PR for Official Notebooks under the notebooks/official folder, follow this mandatory checklist:

[x] Use the notebook template as a starting point.
[x] Follow the style and grammar rules outlined in the above notebook template.
[x] Verify the notebook runs successfully in Colab since the automated tests cannot guarantee this even when it passes.
[x] Passes all the required automated checks. You can locally test for formatting and linting with these instructions.
[ ] You have consulted with a tech writer to see if tech writer review is necessary. If so, the notebook has been reviewed by a tech writer, and they have approved it.
[ ] This notebook has been added to the CODEOWNERS file under the Official Notebooks section, pointing to the author or the author's team.
[x] The Jupyter notebook cleans up any artifacts it has created (datasets, ML models, endpoints, etc) so as not to eat up unnecessary resources.