src: Revert nix stdin _readableState.reading

This reverts 8cee8f5 which was causing a regression through a possible
race condition on Windows 8 and 10.

Fixes: nodejs#2996
Fixes: nodejs#2504

Author: silverwind

src/node.js

@@ -726,7 +726,7 @@
       // not-reading state.
       if (stdin._handle && stdin._handle.readStop) {
         stdin._handle.reading = false;
-        stdin.push('');
+        stdin._readableState.reading = false;
         stdin._handle.readStop();
       }
 
@@ -735,7 +735,7 @@
       stdin.on('pause', function() {
         if (!stdin._handle)
           return;
-        stdin.push('');
+        stdin._readableState.reading = false;
         stdin._handle.reading = false;
         stdin._handle.readStop();
       });