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

@@ -73,14 +73,9 @@ class Printer
      */
     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.
      *