docs: revised create_partitioned_table sample

[thejaredchapman]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Towards #790 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/snippets/create_partitioned_table.py:19, tag bigquery_create_table_partitioned

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[tswast]

Kokoro test failures are real ones in this case:

nox > Running session mypy_samples
nox > Creating virtual environment (virtualenv) using python3.8 in .nox/mypy_samples
nox > python -m pip install -e '.[all]'
nox > python -m pip install pytest
nox > python -m pip install -r /tmpfs/src/github/python-bigquery/samples/geography/requirements.txt
nox > python -m pip install -r /tmpfs/src/github/python-bigquery/samples/snippets/requirements.txt
nox > python -m pip install -r /tmpfs/src/github/python-bigquery/samples/magics/requirements.txt
nox > python -m pip install mypy==0.910
nox > python -m pip install types-mock types-pytz types-protobuf types-python-dateutil types-requests types-setuptools
nox > python -m pip install typing-extensions
nox > mypy --config-file /tmpfs/src/github/python-bigquery/samples/mypy.ini --no-incremental samples/
samples/snippets/create_partitioned_table_test.py:32: error: Name "client" is not defined
samples/snippets/create_partitioned_table_test.py:32: error: Name "to_delete" is not defined
samples/snippets/create_partitioned_table_test.py:34: error: Name "table" is not defined
samples/snippets/create_partitioned_table_test.py:35: error: Name "table" is not defined
samples/snippets/create_partitioned_table_test.py:36: error: Name "table" is not defined
Found 5 errors in 1 file (checked 222 source files)
nox > Command mypy --config-file /tmpfs/src/github/python-bigquery/samples/mypy.ini --no-incremental samples/ failed with exit code 1
nox > Session mypy_samples failed.

Need to update the sample & tests to use the new fixtures.