Drop constraints already defined in airflow itself

• The sqlalchemy constraint is defined here https://github.com/apache/airflow/blob/main/hatch_build.py#L436
• The wtforms constraint was dropped in https://github.com/apache/airflow/pull/43309 after https://github.com/pallets-eco/wtforms/issues/861 was fixed.

This allows us to delegate more of the base dependency version solving to airflow upstream, and avoid having to remember why we have certain constraints in place.

Signed-off-by: Balthazar Rouberol brouberol@wikimedia.org