docs: clarify handoff() docs, callable not supported (#2116)

Author: ihower

src/agents/handoffs/__init__.py

@@ -208,7 +208,7 @@ def handoff(
     """Create a handoff from an agent.
 
     Args:
-        agent: The agent to handoff to, or a function that returns an agent.
+        agent: The agent to handoff to.
         tool_name_override: Optional override for the name of the tool that represents the handoff.
         tool_description_override: Optional override for the description of the tool that
             represents the handoff.

src/agents/realtime/handoffs.py

@@ -74,7 +74,7 @@ def realtime_handoff(
     """Create a handoff from a RealtimeAgent.
 
     Args:
-        agent: The RealtimeAgent to handoff to, or a function that returns a RealtimeAgent.
+        agent: The RealtimeAgent to handoff to.
         tool_name_override: Optional override for the name of the tool that represents the handoff.
         tool_description_override: Optional override for the description of the tool that
             represents the handoff.