GitLab

 * remove spurious .rubocop.yml override files
 * split the configuration into an enforced and optional
 * run both configurations in jenkins (may result in some duplicate
   comments at different levels)
 * auto-correct the enforced configuration in the pre-commit hook
 * fix comments for Gemfile.d and the root dir; enforced configuration
   is only applied to that directory for now

Change-Id: I8da21073d74e19138b1b580d66c7aae6465348d4
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/273898

Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>