remove deprecated stmt key, remove deprecated rule

Author: TomasVotruba

rules/TypeDeclaration/Rector/Expression/InlineVarDocTagToAssertRector.php

@@ -149,13 +149,6 @@ final class AttributeKey
      */
     public const IS_BYREF_RETURN = 'is_byref_return';
 
-    /**
-     * @deprecated This value can change, as based on default input keys. Use existing array keys instead.
-     *
-     * @var string
-     */
-    public const STMT_KEY = 'stmt_key';
-
     /**
      * @var string
      */