Reverted commit D3430206

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](https://github.com/facebook/react-devtools/issues/229).
Closes https://github.com/facebook/react-native/pull/8095

Reviewed By: bestander

Differential Revision: D3430206

Pulled By: javache

fbshipit-source-id: 76f19407271a3779e12bd244f1bc31ef3a8659c7

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -213,7 +213,7 @@ function setUpMapAndSet() {
 function setUpDevTools() {
   if (__DEV__) {
     // not when debugging in chrome
-    if (!window.document) {
+    if (!window.document && require('Platform').OS === 'ios') {
       const setupDevtools = require('setupDevtools');
       setupDevtools();
     }