fix: remove developer notes from transfer_to_agent docstring

The function docstring included a Note section with developer guidance
about using TransferToAgentTool instead. Since this docstring is sent
to the model as the tool description on every invocation, the extra
text wastes input tokens and increases hallucination risk.

Removed the Note section while keeping the user-facing description
and Args documentation intact.

Fixes #4615

Author: stakeswky

src/google/adk/tools/transfer_to_agent_tool.py

@@ -26,14 +26,9 @@
 def transfer_to_agent(agent_name: str, tool_context: ToolContext) -> None:
   """Transfer the question to another agent.
 
-  This tool hands off control to another agent when it's more suitable to
+  Use this tool to hand off control to another agent that is more suitable to
   answer the user's question according to the agent's description.
 
-  Note:
-    For most use cases, you should use TransferToAgentTool instead of this
-    function directly. TransferToAgentTool provides additional enum constraints
-    that prevent LLMs from hallucinating invalid agent names.
-
   Args:
     agent_name: the agent name to transfer to.
   """