Remove ignored string in phpstan rules

rules/phpstan-rules.neon

@@ -4,7 +4,6 @@ includes:
 parameters:
     ignoreErrors:
         - '#Method MDMysqli::_check_query_efficiency\(\) is unused.#'
-        - '# with null as default value.#'
     polluteScopeWithLoopInitialAssignments: false
     polluteScopeWithAlwaysIterableForeach: false
     checkAlwaysTrueCheckTypeFunctionCall: true