Remove iOS platform check for running devtools

Summary:
Currently, DevTools only work under ios (although this is undocumented!),
because the JavaScriptEngine initialization process skips setupDevTools() on
android.

DevTools work fine with Android, as tested on 0.26, 0.27, and 0.28 using
Nuclide's inspector.

For reference, the relevant issue on react-devtools.
Closes https://github.com/facebook/react-native/pull/8095

Reviewed By: bestander

Differential Revision: D3492788

Pulled By: andreicoman11

fbshipit-source-id: 1eda9196d7125da19a8d7baaab22b61b744ca629

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -200,7 +200,7 @@ function setUpCollections(): void {
 function setUpDevTools(): void {
   if (__DEV__) {
     // not when debugging in chrome
-    if (!window.document && require('Platform').OS === 'ios') {
+    if (!window.document) {
       const setupDevtools = require('setupDevtools');
       setupDevtools();
     }