Drop polyfill that are not needed since PHP 7.2

src/PhpSpreadsheet/Chart/Renderer/JpGraph.php

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

src/PhpSpreadsheet/Chart/Renderer/Polyfill.php

@@ -1,9 +0,0 @@
-<?php
-
-// This is a dirty workaround to output JpGraph charts even when antialiasing is not available
-if (!function_exists('imageantialias')) {
-    function imageantialias(...$args): void
-    {
-        // Do nothing
-    }
-}