Remove deprecated option of nullable_type_declaration_for_default_null_value

Author: paulbalandan

src/CodeIgniter4.php

@@ -345,7 +345,7 @@ public function __construct()
             'not_operator_with_space'                          => false,
             'not_operator_with_successor_space'                => true,
             'nullable_type_declaration'                        => false, // requires 8.0+
-            'nullable_type_declaration_for_default_null_value' => ['use_nullable_type_declaration' => true],
+            'nullable_type_declaration_for_default_null_value' => true,
             'numeric_literal_separator'                        => false,
             'object_operator_without_whitespace'               => true,
             'octal_notation'                                   => false, // requires 8.1+