bpo-39639: Remove the AST "Suite" node and associated code (GH-18513)

The AST "Suite" node is no longer used and it can be removed from the ASDL definition and related structures (compiler, visitors, ...).

Co-Authored-By: Victor Stinner <vstinner@python.org>
Co-authored-by: Brett Cannon <54418+brettcannon@users.noreply.github.com>
Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>