Add code comment as requested during PR review

Author: rodrigoprimo

WordPress/Tests/Security/EscapeOutputUnitTest.1.inc

@@ -679,6 +679,9 @@ readonly class( $unescaped ) {}; // Bad.
 
 /*
  * Safeguard correct handling of all types of namespaced function calls when *::class is used.
+ *
+ * Note: using ::class on fully qualified or namespace relative class names doesn't provide
+ * any real value in practice.
  */
 _deprecated_function( __METHOD__, 'x.x.x', \ClassName::class ); // OK.
 die( \MyNamespace\ClassName::class . ' has been abandoned' ); // OK.