conversations: remove broken "discussion replies" link

fixes CNVS-11987

test plan:
  * open old conversations
  * open the view dropdown
  * verify that it does not include the "discussion replies" link

Change-Id: Iaeeaa94a62a978a4d30af251c06b51d7855ed246
Reviewed-on: https://gerrit.instructure.com/32278
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Willesen <jonw@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>