Reverted commit D3443980

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: javache

Differential Revision: D3443980

Pulled By: bestander

fbshipit-source-id: ce0f7dd62ae0f7dfe6654380821660f8660318a6

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -220,7 +220,7 @@ function setUpCollections(): void {
 function setUpDevTools(): void {
   if (__DEV__) {
     // not when debugging in chrome
-    if (!window.document) {
+    if (!window.document && require('Platform').OS === 'ios') {
       const setupDevtools = require('setupDevtools');
       setupDevtools();
     }