refactor: remove redundant clear() call in terminate()

After popping all items from _sse_stream_writers dict, the clear() call
is redundant since the dict is already empty. This is a minor cleanup
with no functional change.

Author: weiguangli-io

src/mcp/server/streamable_http.py

@@ -791,9 +791,6 @@ async def terminate(self) -> None:
             if writer:
                 writer.close()
 
-        # Clear the SSE stream writers dictionary
-        self._sse_stream_writers.clear()
-
         # We need a copy of the keys to avoid modification during iteration
         request_stream_keys = list(self._request_streams.keys())