Remove ‘Regions of England’ library

It made for a good early demo to show how we could have different
libraries, but we’d don’t think there’s a strong user need for being
able to broadcast to a region of England.

Regions also have the problem that:
- they are ambiguous – both England and Scotland have a region called
  ‘South east’
- Northern Ireland doesn’t have formal regions

This commit removes the regions library.

tests/app/main/views/test_broadcast.py

@@ -295,7 +295,6 @@ def test_choose_broadcast_library_page(
         'Counties and Unitary Authorities in England and Wales',
         'Countries',
         'Electoral Wards of the United Kingdom',
-        'Regions of England',
     ])
 
     assert normalize_spaces(page.select('.file-list-hint-large')[1].text) == (