delete outdated json string ids hack

Test plan:
  try changing the group on an assignment, make sure the proper group is
  still selected when you go back to edit

Change-Id: I6dd69b6728ef3059b0cfb9a59ed96a261901cc1b
Reviewed-on: https://gerrit.instructure.com/32718
Reviewed-by: Cameron Sutter <csutter@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>

Author: cmatheson

app/coffeescripts/views/assignments/GroupCategorySelector.coffee

@@ -32,12 +32,6 @@ define [
     @optionProperty 'groupCategories'
     @optionProperty 'nested'
 
-    initialize: ->
-      super
-
-      # delete this after Ifa654f7d853fd167d5bfbaee6184657209d58272 hits prod
-      gc.id = gc.id.toString() for gc in @groupCategories
-
     showGroupCategoryCreateDialog: =>
       if @$groupCategoryID.val() == 'new'
         # TODO: Yikes, we need to pull the javascript out of manage_groups.js