Fix BlockTransformer Py3 issues (#21376)

Django's reverse can handle Unicode for arguments.

cms/lib/xblock/runtime.py

@@ -17,7 +17,7 @@ def handler_url(block, handler_name, suffix='', query='', thirdparty=False):
         raise NotImplementedError("edX Studio doesn't support third-party xblock handler urls")
 
     url = reverse('component_handler', kwargs={
-        'usage_key_string': six.text_type(block.scope_ids.usage_id).encode('utf-8'),
+        'usage_key_string': six.text_type(block.scope_ids.usage_id),
         'handler': handler_name,
         'suffix': suffix,
     }).rstrip('/')