Issue #3386929: Remove root namespace native DebugClassLoader forward compatibility warnings

core/.deprecation-ignore.txt

@@ -18,10 +18,6 @@
 %Method "Twig\\NodeVisitor\\NodeVisitorInterface::[^"]+" might add "[^"]+" as a native return type declaration in the future. Do the same in (child class|implementation) "[^"]+" now to avoid errors or add an explicit @return annotation to suppress this message%
 %Method "Twig\\TokenParser\\TokenParserInterface::[^"]+" might add "[^"]+" as a native return type declaration in the future. Do the same in (child class|implementation) "[^"]+" now to avoid errors or add an explicit @return annotation to suppress this message%
 
-# Skip root namespace native DebugClassLoader forward compatibility warnings.
-# These mostly refer to PHP native classes, could be fixed for PHP 8.1.
-%Method "[^\\]+::\w+\(\)" might add "[^"]+" as a native return type declaration in the future. Do the same in (child class|implementation) "[^"]+" now to avoid errors or add an explicit @return annotation to suppress this message%
-
 # The following deprecation is listed for Twig 2 compatibility when unit
 # testing using \Symfony\Component\ErrorHandler\DebugClassLoader.
 %The "Twig\\Environment::getTemplateClass\(\)" method is considered internal\. It may change without further notice\. You should not extend it from "Drupal\\Core\\Template\\TwigEnvironment"\.%