Update admin.py
Update admin.py

I removed a column with the approval of the CM team to simplify the view a bit. Column removed is 'is_assessment_errata'

openstax/openstax-cms,openstax/openstax-cms,openstax/openstax-cms,openstax/openstax-cms,Connexions/openstax-cms,Connexions/openstax-cms