[predicates] keep making `yes` predicate importable from cubicweb (closes #2790319) The `yes` predicate was moved out in CubicWeb 3.15 but it should have remained importable from the cubicweb.predicates module, for bw compat reasons and also because logilab.common.registry is an implementation detail.

drop_relation_definition('CWSourceSchemaConfig', 'cw_schema', 'CWAttribute')
sync_schema_props_perms('cw_schema')