Simplify token validation in download handler

- Changed from checkToken() to simple token existence check
- checkToken() does not exist in this Dolibarr version
- Now uses same pattern as other files in the module: if (!token)
- Matches the token validation pattern used in declarationtva_view.php
- Should resolve the PHP Fatal error

download_pdf.php

@@ -30,7 +30,7 @@ $declaration_id = GETPOST('id', 'int');
 $token = GETPOST('token', 'alpha');
 
 // Validate token
-if (!checkToken($token)) {
+if (!$token) {
     accessforbidden();
 }