revert D2372548 to fix initial app state issue

Reviewed By: @hedgerwang

Differential Revision: D2480492

React/Modules/RCTAppState.m

@@ -101,13 +101,4 @@ RCT_EXPORT_METHOD(getCurrentAppState:(RCTResponseSenderBlock)callback
   callback(@[@{@"app_state": _lastKnownState}]);
 }
 
-#pragma mark - RCTBridgeModule
-
-- (NSDictionary *)constantsToExport
-{
-  return @{
-     @"initialAppState" : RCTCurrentAppBackgroundState()
-   };
-}
-
 @end