chore(docs): de-dupe region tag bigquery_query_external_gcs_perm

[meredithslota]

Follow-up to #1648

Fixes#773

Do not merge until cl/565816568 is submitted.

[snippet-bot]

You are about to delete the following sample browser page.

• docs/snippets.py:628, tag bigquery_query_external_gcs_perm(usage: page 1).

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You are about to delete the following frozen region tag.

• docs/snippets.py:628, tag bigquery_query_external_gcs_perm(usage: page 1).

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Here is the summary of changes.

You are about to delete 1 region tag.

• docs/snippets.py:628, tag bigquery_query_external_gcs_perm

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[meredithslota]

cl/566316539 has been submitted which addresses the frozen region tag note above.