docs: stop presenting the in-memory client as the way to connect (#3443)

docs_src/extensions/tutorial003.py

@@ -1,7 +1,6 @@
 from collections.abc import Sequence
 from typing import Any
 
-from mcp import Client
 from mcp.server.extension import Extension, ToolBinding
 from mcp.server.mcpserver import MCPServer
 
@@ -24,12 +23,3 @@ class Stamps(Extension):
 
 
 mcp = MCPServer("post-office", extensions=[Stamps()])
-
-
-async def main() -> None:
-    async with Client(mcp) as client:
-        print(client.server_capabilities.extensions)
-        # {'com.example/stamps': {'sealed': True}}
-        result = await client.call_tool("stamp", {"text": "hello"})
-        print(result.content)
-        # [TextContent(text='[stamped] hello')]