Revert "create PermissionsSerializer for serializing permissions"

This reverts commit cf8716bfb0095efcff4e706d88320b3c2acdc7d8.

Change-Id: I7c58b7533d2d34c4ddb3fd4d3f491b1656f71d84
Reviewed-on: https://gerrit.instructure.com/29135
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>