Deprecates version of%%bigquery magic in this package.

Note: I keep the implementation intact to reduce disruption for folks that don't install theipython extras.

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 abug/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)

Fixesgoogleapis/python-bigquery-magics#14
🦕