fix: drop unused EVENT_ID_MARKER constant

Author: benedikt-bartscher

reflex/event.py

@@ -89,7 +89,6 @@ def substate_token(self) -> str:
 _EVENT_FIELDS: set[str] = {f.name for f in dataclasses.fields(Event)}
 
 BACKGROUND_TASK_MARKER = "_reflex_background_task"
-EVENT_ID_MARKER = "_rx_event_id"
 EVENT_ACTIONS_MARKER = "_rx_event_actions"
 
 
@@ -2313,7 +2312,6 @@ class EventNamespace:
 
     # Constants
     BACKGROUND_TASK_MARKER = BACKGROUND_TASK_MARKER
-    EVENT_ID_MARKER = EVENT_ID_MARKER
     EVENT_ACTIONS_MARKER = EVENT_ACTIONS_MARKER
     _EVENT_FIELDS = _EVENT_FIELDS
     FORM_DATA = FORM_DATA