CI: adapt schema tool to recent releases of pyyaml

Don't import a specific draft validator (it isn't used anyway,
and the validator is picked up from the schema's version)

ci/configvalidator.py

@@ -48,7 +48,6 @@ ERR_IMPORT, ERR_USAGE, ERR_FILE_NOT_FOUND, ERR_SYNTAX, ERR_INVALID = range(1,6)
 #
 try:
     from jsonschema import validate, SchemaError, ValidationError
-    from jsonschema import draft7_format_checker
     from yaml import safe_load, YAMLError
 except ImportError as e:
     print(e)