added tests for submission details partial

added tests and removed secondary speedgrader link that caused error

fixes CNVS-8868

test plan
- set large_roster flag to true for a course
- go to gradebook and click the text bubble on a submitted assignment
- link to speedgrader should not appear
- set large_roster flag to false
- only one link to speedgrader should appear

Change-Id: I0bfb5452a8adddb140fe80b0ee12b82b2249dc3c
Reviewed-on: https://gerrit.instructure.com/38503
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>