always show "Courses" instead of "Home" in global nav tab

test plan:
* confirm that all users have "Courses" in the top global
navigation (instead of "Home")

fixes #CNVS-9701

Change-Id: Idc9200e5a55d8010b3cc7df61592c23b78056389
Reviewed-on: https://gerrit.instructure.com/36730
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>