Remove buffer size argument (#232)

- We're removing the buffer arugment from the API as a result of a mini review. This is a pre-emptive reaction to avoid breakage when the change comes in.

src/Microsoft.AspNetCore.WebSockets/WebSocketMiddleware.cs

@@ -119,10 +119,7 @@ namespace Microsoft.AspNetCore.WebSockets
 
                 Stream opaqueTransport = await _upgradeFeature.UpgradeAsync(); // Sets status code to 101
 
-                // Allocate a buffer for receive (default is 4k)
-                var buffer = new byte[receiveBufferSize];
-
-                return WebSocketProtocol.CreateFromStream(opaqueTransport, isServer: true, subProtocol: subProtocol, keepAliveInterval: keepAliveInterval, buffer: buffer);
+                return WebSocketProtocol.CreateFromStream(opaqueTransport, isServer: true, subProtocol: subProtocol, keepAliveInterval: keepAliveInterval);
             }
         }
     }