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

Summary:
Fixes #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: https://github.com/facebook/react-native/pull/22290

Differential Revision: D13374345

Pulled By: cpojer

fbshipit-source-id: 1173241f2b6912fd6df5e196053a950bb42ff01b

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

@@ -357,7 +357,7 @@ public final class WebSocketModule extends ReactContextBaseJavaModule {
           requestURI.getHost(),
           requestURI.getPort());
       } else {
-        defaultOrigin = String.format("%s://%s/", scheme, requestURI.getHost());
+        defaultOrigin = String.format("%s://%s", scheme, requestURI.getHost());
       }
 
       return defaultOrigin;