chore: remove unused variable assignment

Signed-off-by: Yves Bastide <yves@botify.com>

Author: ybastide

simpleflow/swf/mapper/models/event/factory.py

@@ -127,7 +127,7 @@ def _extract_event_state(cls, event_type: str, event_name: str) -> str:
             Returns: 'start_initiated'
 
         """
-        left, sep, right = event_name.partition(event_type)
+        left, _, right = event_name.partition(event_type)
         return camel_to_underscore(left + right)