fix: Drop misleading "conversation history" example from server-ai README

`ManagedModel.get_config().messages` returns the configured/templated
system messages from the AI Config, not the conversation history the
model accumulated across run() calls. Drop the block rather than imply
otherwise.

Refs AIC-2383

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jsonbailey

packages/sdk/server-ai/README.md

@@ -129,10 +129,6 @@ async def main():
 
         response2 = await model.run("What's the status?")
         print(response2.content)
-        
-        # Access conversation history
-        messages = model.get_config().messages
-        print(f'Conversation has {len(messages)} messages')
 
 asyncio.run(main())
 ```