Clean up CallbackRegistry

There were some ancient code there.

atom/browser/lib/rpc-server.coffee

@@ -71,7 +71,7 @@ unwrapArgs = (sender, args) ->
         ret = ->
           if rendererReleased
             throw new Error("Attempting to call a function in a renderer window
-             that has been closed or released. Function provided here: #{meta.id}.")
+              that has been closed or released. Function provided here: #{meta.id}.")
           sender.send 'ATOM_RENDERER_CALLBACK', meta.id, valueToMeta(sender, arguments)
         v8Util.setDestructor ret, ->
           return if rendererReleased

atom/common/api/lib/callbacks-registry.coffee

@@ -1,16 +1,11 @@
-savedGlobal = global  # the "global.global" might be deleted later
-
 module.exports =
 class CallbacksRegistry
   constructor: ->
-    @emptyFunc = -> throw new Error "Browser trying to call a non-exist callback
-      in renderer, this usually happens when renderer code forgot to release
-      a callback installed on objects in browser when renderer was going to be
-      unloaded or released."
+    @nextId = 0
     @callbacks = {}
 
   add: (callback) ->
-    id = Math.random().toString()
+    id = ++@nextId
 
     # Capture the location of the function and put it in the ID string,
     # so that release errors can be tracked down easily.
@@ -32,10 +27,10 @@ class CallbacksRegistry
     @callbacks[id] ? ->
 
   call: (id, args...) ->
-    @get(id).call savedGlobal, args...
+    @get(id).call global, args...
 
   apply: (id, args...) ->
-    @get(id).apply savedGlobal, args...
+    @get(id).apply global, args...
 
   remove: (id) ->
     delete @callbacks[id]