hides discussion publish status on student's edit page

fixes CNVS-11935

test plan
- as a student, create a discussion topic
- ensure that "Not Published" is not displayed on the top right
 of the discussion edit page
- edit the new discussion
- ensure that "Published" is not displayed on the top right of
 the discussion edit page

Change-Id: I5bae83750c16a368bf4d6c58c850d23fa3c7e883
Reviewed-on: https://gerrit.instructure.com/32163
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Reviewed-by: Braden Anderson <banderson@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>