Enable the quitAndInstall to be cancelled by beforeunload handler.

renderer/lib/init.coffee

@@ -50,16 +50,6 @@ window.onerror = (error) ->
   else
     false
 
-# Enable browser to close window silently.
-setTimeout ->
-  require('ipc').once 'ATOM_SHELL_SILENT_CLOSE', ->
-    window.onbeforeunload = null
-    window.close()
-
-# Override default window.close.
-window.close = ->
-  require('remote').getCurrentWindow().close()
-
 # Override default window.open.
 window.open = (url, name, features) ->
   options = {}