[minor] Remove setEncoding on incoming socket

This isn't needed as we don't do any string operations and `setEncoding`
results in a higher memory usage and is slower.

lib/node-http-proxy/http-proxy.js

@@ -452,9 +452,6 @@ HttpProxy.prototype.proxyWebSocketRequest = function (req, socket, head, buffer)
         socket.pair.cleartext.socket.setKeepAlive(true, 0);
       }
     }
-    else {
-      socket.setEncoding('utf8');
-    }
   }
 
   //