Issue #3271498: Remove xmlrpc test dependency

This is not used in testing and only used at all for FillPDF Service,
which is deprecated.

This was commented-out in db4154d7.

fillpdf.info.yml

@@ -12,5 +12,3 @@ dependencies:
   - drupal:options
 test_dependencies:
   - webform:webform
-  # xmlrpc does not have a Drupal 9 release yet.
-  # - xmlrpc:xmlrpc