remove unused patch to ActionController::Session::AbstractStore::SessionHash

fixes CNVS-12175

Change-Id: Ie93e7fb82ad95a827c832bcc912895f03ec4c826
Reviewed-on: https://gerrit.instructure.com/32400
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>
QA-Review: Simon Williams <simon@instructure.com>