MDL-60301 assignfeedback_editpdf: changes to files after FPDI update

1) Change the fpdi_bridge class so that it extends the pdf class,
rather than the TCPDF class.
2) Empty class check that was implemented before
3) Updated the editpdf/fpdi/readme_moodle.txt file to document the changes.
4) Updated the editpdf/thirdpartylibs.xml to reflect the update to the
FPDI library.

mod/assign/feedback/editpdf/fpdi/fpdi_bridge.php

@@ -16,21 +16,12 @@
  * This way it is possible to use FPDI for both FPDF and TCPDF with one FPDI version.
  */
 
-if (!class_exists('TCPDF', false)) {
     /**
      * Class fpdi_bridge
+     *
+     * This has been modified to use the Moodle pdf class which in turn extends the TCPDF class.
      */
-    class fpdi_bridge extends FPDF
-    {
-        // empty body
-    }
-
-} else {
-
-    /**
-     * Class fpdi_bridge
-     */
-    class fpdi_bridge extends TCPDF
+    class fpdi_bridge extends pdf
     {
         /**
          * Array of Tpl-Data
@@ -203,4 +194,3 @@ public function str2hex($str)
             return current(unpack('H*', $str));
         }
     }
-}