Revert callsites to PdfExportHook assume use of HookEssentials

fd6a977 introduced HookEssentials to PdfExport
ea38305 changed the callsites to use HookEssentials
be0a311 reverted the change to PdfExport to stay compatible with the
original implementation but failed to remove the callsites

This commit reverts the changes to the call sites made in ea38305

Author: TheSyscall

library/Icinga/File/Pdf.php

@@ -8,6 +8,7 @@
 use Dompdf\Dompdf;
 use Dompdf\Options;
 use Exception;
+use Icinga\Application\Hook;
 use Icinga\Application\Hook\PdfexportHook;
 use Icinga\Application\Icinga;
 use Icinga\Exception\ProgrammingError;
@@ -56,7 +57,7 @@ public function renderControllerAction($controller)
 
         $request = $controller->getRequest();
 
-        if (PdfexportHook::isRegistered()) {
+        if (Hook::has('Pdfexport')) {
             $pdfexport = PdfexportHook::first();
             $pdfexport->streamPdfFromHtml($html, sprintf(
                 '%s-%s-%d',

library/Icinga/Web/Widget/Tabextension/OutputFormat.php

@@ -5,7 +5,6 @@
 
 namespace Icinga\Web\Widget\Tabextension;
 
-use Icinga\Application\Hook\PdfexportHook;
 use Icinga\Application\Platform;
 use Icinga\Application\Hook;
 use Icinga\Web\Url;
@@ -85,7 +84,7 @@ public function getSupportedTypes()
     {
         $supportedTypes = array();
 
-        $pdfexport = PdfexportHook::isRegistered();
+        $pdfexport = Hook::has('Pdfexport');
 
         if ($pdfexport || Platform::extensionLoaded('gd')) {
             $supportedTypes[self::TYPE_PDF] = array(