don't return localized enrollment type in courses api

test plan:
 - have a user whose language is something other than english
 - enroll that user in a course
 - use the courses API as that user
 - the returned enrollment types should be "teacher", "student", etc.
   and not a localized enrollment type
 - consult enrollment api docs: the "type" and "role" fields
   should not have an identical description

fixes CNVS-12065

Change-Id: I572ecd0d9bdadb0da00fe3d8b7359645ad59e183
Reviewed-on: https://gerrit.instructure.com/32550
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>