Remove Platform check from WebSocket module

Summary:
WebSocket uses the Platform module to check how many arguments for the `close` method should be used. In react-native-windows, we have the same number of arguments for `close` as Android, so we're prevented from using this module as-is because of the platform check (see https://github.com/Microsoft/react-native-windows/blob/master/Libraries/WebSocket/WebSocket.windows.js#L136).

By switching to an argument count check, this module becomes more useful cross-platform. If you'd like to keep the platform check, I'm also open to inverting the conditional, e.g., `if (Platform.OS !== 'ios')`.

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I'd like to minimize the amount of code I need to copy over to react-native-windows for platform-specific overrides.

Run jest tests.

N/A

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
[GENERAL][MINOR][ENHANCEMENT][Libraries/WebSocket/WebSocket.js] - Better enable cross-platform support of WebSocket.js
Closes facebook#18056

Differential Revision: D7070380

Pulled By: TheSavior

fbshipit-source-id: 9bfd47654d0bf6f0e07fc799853a206721467525

Author: rozele

Libraries/WebSocket/WebSocket.js

@@ -14,7 +14,6 @@ const EventTarget = require('event-target-shim');
 const NativeEventEmitter = require('NativeEventEmitter');
 const BlobManager = require('BlobManager');
 const NativeModules = require('NativeModules');
-const Platform = require('Platform');
 const WebSocketEvent = require('WebSocketEvent');
 
 /* $FlowFixMe(>=0.54.0 site=react_native_oss) This comment suppresses an error
@@ -203,7 +202,7 @@ class WebSocket extends EventTarget(...WEBSOCKET_EVENTS) {
   }
 
   _close(code?: number, reason?: string): void {
-    if (Platform.OS === 'android') {
+    if (WebSocketModule.close.length === 3) {
       // See https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent
       const statusCode = typeof code === 'number' ? code : CLOSE_NORMAL;
       const closeReason = typeof reason === 'string' ? reason : '';