docs: remove unused query code sample (#1769)

* docs: remove unused query code sample

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

* remove sample test too

* update reference to query() sample in usage guides

---------

Co-authored-by: Kira <[email protected]>

Author: tswast

docs/usage/queries.rst

@@ -5,9 +5,9 @@ Querying data
 ^^^^^^^^^^^^^
 
 Run a query and wait for it to finish with the
-:func:`~google.cloud.bigquery.client.Client.query` method:
+:func:`~google.cloud.bigquery.client.Client.query_and_wait` method:
 
-.. literalinclude:: ../samples/client_query.py
+.. literalinclude:: ../samples/snippets/client_query.py
    :language: python
    :dedent: 4
    :start-after: [START bigquery_query]