Remove unused constant HANDLER_SUPPORTS_TRIGGERER (#49370)

This was obsoleted by logging changes in task sdk, but its removal was missed, it seems.

Author: dstandish

airflow-core/src/airflow/jobs/triggerer_job_runner.py

@@ -81,14 +81,6 @@
     from airflow.sdk.types import RuntimeTaskInstanceProtocol as RuntimeTI
     from airflow.triggers.base import BaseTrigger
 
-HANDLER_SUPPORTS_TRIGGERER = False
-"""
-If this value is true, root handler is configured to log individual trigger messages
-visible in task logs.
-
-:meta private:
-"""
-
 logger = logging.getLogger(__name__)
 
 __all__ = [