DOC: Remove reference to mysql fallback support from user guide. (#51275)

Remove reference to mysql fallback support from user guide.

Co-authored-by: Chuck Cadman <[email protected]>

Author: cdcadman

doc/source/user_guide/io.rst

@@ -5498,11 +5498,8 @@ included in Python's standard library by default.
 You can find an overview of supported drivers for each SQL dialect in the
 `SQLAlchemy docs <https://docs.sqlalchemy.org/en/latest/dialects/index.html>`__.
 
-If SQLAlchemy is not installed, a fallback is only provided for sqlite (and
-for mysql for backwards compatibility, but this is deprecated and will be
-removed in a future version).
-This mode requires a Python database adapter which respect the `Python
-DB-API <https://www.python.org/dev/peps/pep-0249/>`__.
+If SQLAlchemy is not installed, you can use a :class:`sqlite3.Connection` in place of
+a SQLAlchemy engine, connection, or URI string.
 
 See also some :ref:`cookbook examples <cookbook.sql>` for some advanced strategies.