Migration for change of DFE sectors

Adding safeguarding-children to both DFE parent sectors and removing
Procurement from schools-colleges. Relates to
https://www.pivotaltracker.com/story/show/67759054
Merge pull request #142 from alphagov/change-to-dfe-sectors

Migration for change of DFE sectors

https://www.pivotaltracker.com/story/show/67759054