change Validate Links in Content header from h2 to h1
change Validate Links in Content header from h2 to h1

fixes ADMIN-1280

test plan:
- Navigate to the Course Settings page
- Click on "Validate Links in Content"
- Inspect the heading and note that it's an h1

Change-Id: Id253d2e0d489617ea0ea63927ddcb5084ca46189
Reviewed-on: https://gerrit.instructure.com/158711
Product-Review: Dan Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
QA-Review: Dan Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Tested-by: Jenkins

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms