Removes the customize functionality from the courses menu

Removes customization from the courses dropdown menu.  Combines the
customize and the view all courses link.

closes CNVS-14682

test plan:
   - Open up Canvas and hover over the Courses
   - The link next to the My Courses title should say
      "View All or Customize (##)"
   - Clicking on the link should take you the My Courses page

Change-Id: Ic1a3923908393664a33709c683550d8fd12daad1
Reviewed-on: https://gerrit.instructure.com/39090
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>