Updates the drag & drop accessibility warning

fixes CNVS-15277

Test Plan:
  - Go to the modules page (/courses/##/modules)
  - When using keyboard navigation, when you get to a drag &
    drop handle, a warning should appear with the text:
    "Warning: For improved accessibility in reordering Modules
    (or Module items), please use the Move To Dialog option
    found in the menu."
  - Go to the course settings page (/courses/##/settings)
  - Using keyboard navigation, when you tab into the
    navigation tab, a warning should appear with the text:
    "Warning: For improved accessibility in reordering Course
     Navigation elements, please use the Move To Dialog option
     found in the menu."

Change-Id: I3e2b6a295f1e63099e5a90fef3ce96b63980b937
Reviewed-on: https://gerrit.instructure.com/40629
QA-Review: Clare Strong <clare@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>