Remove trailing slash from origin header if no port is specified (facebook#22290)

Summary:
Fixes facebook#16304

The standard format for origin HTTP headers does not allow a trailing slash. In order to not get warnings when connecting a websocket, I removed the trailing slash when generating the default origin HTTP header for the websocket connect request.

Release Notes:
----------
[Android] [Fixed] - Fixed default origin header for websocket connections to match the standard format (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin) in WebSocketModule
Pull Request resolved: facebook#22290

Differential Revision: D13374345

Pulled By: cpojer

fbshipit-source-id: 1173241f2b6912fd6df5e196053a950bb42ff01b

Author: Lea Bärtschi

ReactAndroid/src/main/java/com/facebook/react/modules/websocket/WebSocketModule.java

@@ -352,7 +352,7 @@ private static String getDefaultOrigin(String uri) {
           requestURI.getHost(),
           requestURI.getPort());
       } else {
-        defaultOrigin = String.format("%s://%s/", scheme, requestURI.getHost());
+        defaultOrigin = String.format("%s://%s", scheme, requestURI.getHost());
       }
 
       return defaultOrigin;