inline only usage of Array#to_atom

Change-Id: I5cf6784b4f858f689e8d707dfced29a02590b9ff
Reviewed-on: https://gerrit.instructure.com/30029
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Raphael Weiner <rweiner@pivotallabs.com>
Product-Review: Raphael Weiner <rweiner@pivotallabs.com>
QA-Review: Raphael Weiner <rweiner@pivotallabs.com>