Delete browser-specific test type

Author: stephentoub

src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs

@@ -137,7 +137,7 @@ public async Task<Connection> EstablishConnectionAsync()
                 Stream stream = null;
 #if TARGET_BROWSER
                 closableWrapper = new SocketWrapper(_listenSocket);
-                stream = new WebSocketStream(_listenSocket, ownsSocket: true);
+                stream = new WebSocketStream(_listenSocket, WebSocketMessageType.Binary, ownsSocket: true);
 #else
                 var socket = await _listenSocket.AcceptAsync().ConfigureAwait(false);
                 closableWrapper = new SocketWrapper(socket);