Remove private constructor for Printer

The Printer is not stateful. So enforcing a singleton serves no purpose (anymore?).

We can easily use `new Printer()->printAST($node)`.

Author: ruudk

src/Language/Printer.php

@@ -70,17 +70,14 @@ class Printer
      * Handles both executable definitions and schema definitions.
      *
      * @api
+     *
+     * @throws \JsonException
      */
     public static function doPrint(Node $ast): string
     {
-        static $instance;
-        $instance ??= new static();
-
-        return $instance->printAST($ast);
+        return (new static())->printAST($ast);
     }
 
-    protected function __construct() {}
-
     /**
      * Recursively traverse an AST depth-first and produce a pretty string.
      *