Drop polyfill that are not needed since PHP 7.2

Author: PowerKiKi

src/PhpSpreadsheet/Chart/Renderer/JpGraph.php

@@ -21,8 +21,6 @@
 use Spline;
 use StockPlot;
 
-require_once __DIR__ . '/Polyfill.php';
-
 class JpGraph implements IRenderer
 {
     private static $width = 640;