chore: update active partitions handler doc comment

Signed-off-by: Vaibhav Tiwari <vaibhav.tiwari33@gmail.com>

Author: vaibhavtiwari33

packages/pynumaflow/pynumaflow/sourcer/_dtypes.py

@@ -301,7 +301,6 @@ async def active_partitions_handler(self) -> PartitionsResponse:
         """
         Returns the active partitions associated with the source, used by the platform
         to determine the partitions to which the watermark should be published.
-        Falls back to partitions_handler() if not overridden.
         """
         pass