move deleted enrollments when cross listing sections

fixes CNVS-13828

test plan
 - prior to checking out patch set
 - enroll a user in a section
 - delete the enrollment
 - cross list the section
 - attempt to add user to sections new course
 - it should fail
 - checkout patch set and run migration
 - attempt to add user to sections new course
 - it should succeed

 - enroll a user in a section
 - delete the enrollment
 - cross list the section
 - attempt to add user to sections new course
 - it should work (it will restore the old enrollment)

 - enroll a user in a cross listed section
 - delete the enrollment
 - uncross list the section
 - attempt to add the user to the sections current course
 - it should work (it will restore the old enrollment)

Change-Id: Ib397f96b0761d87bf6f9fb11ffc978012f0f5b39
Reviewed-on: https://gerrit.instructure.com/37036
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>