remove 'development' flag on sortable name feature

closes CNVS-17621

This commit removes the 'development' bit on the sortable name feature
for the gradebook.

Test plan
- Navigate to course feature flags in a production environment
- The sortable name feature should be visible

Change-Id: I8fe5d340767a97852db272d7bd9509f9b2fe35bf
Reviewed-on: https://gerrit.instructure.com/46178
Product-Review: Bryan Madsen <bryan@instructure.com>
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>