docs: remove unused query code sample

[tswast]

This sample was moved in https://github.com/googleapis/python-bigquery/pull/1722/files#diff-2e8df14049580f42d6c73a3209838b96f3c9b185d2d7f2688683ae60bb2e7c43. Docs updated in internal change 597332356.

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Fixes #<issue_number_goes_here> 🦕

[snippet-bot]

Here is the summary of changes.

You are about to delete 1 region tag.

• samples/client_query.py:20, tag bigquery_query

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