Remove deprecated code

[davidism]

• Some argument to send_file and send_from_directory were renamed in Flask 2.0. The removal of the old names was deferred for an extra release. They have now been issuing a deprecation warning for over a year. download_name replaces attachment_filename, max_age replaces cache_timeout, etag replaces add_etags, and path replaces filename.
• RequestContext.g was a property returning AppContext.g. Since g is not part of the request context, the property is removed.