Rename #before_close to #shutdown

Author: ysbaddaden

src/crystal/system/wasi/socket.cr

@@ -152,7 +152,7 @@ module Crystal::System::Socket
   end
 
   private def system_close
-    event_loop.before_close(self)
+    event_loop.shutdown(self)
     event_loop.close(self)
   end