avoid n-queries loading account users on account settings page

refs CNVS-11420

Change-Id: Ia54b5b3ac528d39b1aad0d4039305786d7bd2dd4
Reviewed-on: https://gerrit.instructure.com/31000
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Anthus Williams <awilliams@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>