revert making close_connection CS shielded, as that would be a behaviour change causing very long stalls with the default timeout of 60s

Author: jakkdl

trio_websocket/_impl.py

@@ -145,8 +145,7 @@ async def open_connection(nursery: trio.Nursery) -> WebSocketConnection:
 
     async def close_connection(connection: WebSocketConnection) -> None:
         try:
-            with trio.fail_after(disconnect_timeout) as cs:
-                cs.shield = True
+            with trio.fail_after(disconnect_timeout):
                 await connection.aclose()
         except trio.TooSlowError:
             raise DisconnectionTimeout from None