Delete Temporary Files In XssVulnerabilityTest (#1800)

* Delete Temporary Files In XssVulnerabilityTest

They need not exist after the test. Some of them are placed in
current directory, which means Git thinks they are needed.

tests/PhpSpreadsheetTests/Writer/Html/XssVulnerabilityTest.php

@@ -43,6 +43,7 @@ class XssVulnerabilityTest extends Functional\AbstractFunctional
         $writer->save($filename);
 
         $verify = file_get_contents($filename);
+        unlink($filename);
         // Ensure that executable js has been stripped from the comments
         self::assertStringContainsString($adjustedTextString, $verify);
     }
@@ -58,8 +59,6 @@ class XssVulnerabilityTest extends Functional\AbstractFunctional
         ];
     }
 
-    private static $counter = 0;
-
     /**
      * @dataProvider providerXssRichText
      *
@@ -84,8 +83,7 @@ class XssVulnerabilityTest extends Functional\AbstractFunctional
         $writer->save($filename);
 
         $verify = file_get_contents($filename);
-        $counter = self::$counter++;
-        file_put_contents("verify{$counter}.html", $verify);
+        unlink($filename);
         // Ensure that executable js has been stripped from the comments
         self::assertStringNotContainsString($xssTextString, $verify);
     }