some optimisations for scheduler api json

refs CNVS-5647

test plan:
 * simple regression test of creating, editing, and signing up
   for appointments

Change-Id: Iee2b30ff2ffcd15e4e0664177052eec0f3e5e22b
Reviewed-on: https://gerrit.instructure.com/33402
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>