chore: remove migrated snippets

[dizcology]

The snippets have been migrated to python-docs-samples (GoogleCloudPlatform/python-docs-samples#10255)) and documentation pages updated (example: https://cloud.google.com/bigquery/docs/reference/bigqueryconnection#use).

[snippet-bot]

You are about to delete the following sample browser pages.

• samples/snippets/create_mysql_connection.py:15, tag bigqueryconnection_create_connection(usage: page 1).
• samples/snippets/quickstart.py:15, tag bigqueryconnection_quickstart(usage: page 1).

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Here is the summary of changes.

You are about to delete 2 region tags.

• samples/snippets/create_mysql_connection.py:15, tag bigqueryconnection_create_connection
• samples/snippets/quickstart.py:15, tag bigqueryconnection_quickstart

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