Rename cleanup_interface_sobjects into cleanup_unused_appobjects Interfaces are gone in 3.18 Related to #2782004.

remove cw 3.9 bw compat (bw compat other than the interface -> adapter changes) - cwconfig, doc/admin/setup: docstring adjustment wrt 3.9 & virtualenv - testing/rst: windmill (which is gone from the testing infrastructure) - other docs: "stuff introduced in 3.9" cleanup, as we don't care about the version old features were introduced - server/hooky.py: bw compat for propagation hooks - server/schemaserial.py: pre CWUniqueTogetherConstraint migration support - web.__init__.py: dumps bw import - autoform.py: .action ppty is gone, also deprecate set_action and get_action - baseviews: CSVView.subvid gone long ago, secondary view removal - primary.py: _render_attribute & _render_relation signature change - reledit.py: rvid/default_value bw compat, should_edit_* dropped - webconfig.py: resourcefile is gone - formfields.py: old vocabulary handling - request.py: build_ajax_replace_url, external_resource Related to #2782004.