Remove window.history.state polyfill

We used it for phantomjs and we're not using phantomjs at the moment (nor we'll
use it after switch to ember-cli)

assets/scripts/travis.coffee

@@ -6,18 +6,6 @@ require 'app'
 window.ENV ||= {}
 window.ENV.RAISE_ON_DEPRECATION = true
 
-if window.history.state == undefined
-  window.history.state = {}
-  oldPushState = window.history.pushState
-  window.history.pushState = (state, title, href) ->
-    window.history.state = state
-    oldPushState.apply this, arguments
-
-  oldReplaceState = window.history.replaceState
-  window.history.replaceState = (state, title, href) ->
-    window.history.state = state
-    oldReplaceState.apply this, arguments
-
 # TODO: how can I put it in Travis namespace and use immediately?
 Storage = Em.Object.extend
   init: ->