Fix output file deletion after exception thrown on write (#328)

For relative paths, it would not work as the FileSystemHelper would not allow deleting a file that's not part of its base folder.

src/Spout/Common/Helper/GlobalFunctionsHelper.php

@@ -203,18 +203,6 @@ class GlobalFunctionsHelper
         return (strpos($path, 'zip://') === 0);
     }
 
-    /**
-     * Wrapper around global function dirname()
-     * @see dirname()
-     *
-     * @param string $filePath
-     * @return string
-     */
-    public function dirname($filePath)
-    {
-        return dirname($filePath);
-    }
-
     /**
      * Wrapper around global function feof()
      * @see feof()