remove containment for sortable modules

this allows tall modules to be dragged to the bottom of the list

fixes CNVS-22525

test plan:
 - make a few modules
 - add a few module items to one of the modules to make it
   taller
 - with the tall module open, drag it to the bottom of the
   module list to put it at the bottom

Change-Id: I96047e68a044fd1b48b62a4d45a1787f200cbf1e
Reviewed-on: https://gerrit.instructure.com/64599
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Jon Willesen <jonw@instructure.com>

public/javascripts/context_modules.js

@@ -1311,7 +1311,6 @@ define([
       $("#context_modules").sortable({
         handle: '.reorder_module_link',
         helper: 'clone',
-        containment: '#context_modules_sortable_container',
         axis: 'y',
         update: modules.updateModulePositions
       });