removed useless view original link

fixes CNVS-3160

test plan:
  - as teacher create assignment with online text submission
  - submit the assignment as a student
  - go to assignment details page
  - "view the original entry" link shouldn't show up

Change-Id: I4ddd9c9cd504e9ec96bcc2b85843ed2216846117
Reviewed-on: https://gerrit.instructure.com/33660
Reviewed-by: Coraline Ehmke <coraline@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>