Fix tests broken by GOV.UK Frontend template

Fix test broken by removal of GOV.UK logo image
- tests/app/main/views/test_notifications.py

Fix tests that ref GOV.UK template CSS files
- tests/app/main/views/test_index.py

Fix test broken by govuk-visually-hidden
- tests/app/main/views/test_send.py

Fix tests broken by header menu link -> button
- tests/app/main/views/test_service_settings.py
- tests/app/main/views/test_template_folders.py

Fix tests broken by removing div#content
- tests/app/main/views/accounts/test_choose_accounts.py
- tests/app/test_navigation.py

Remove references to GOV.UK CSS
- tests/app/main/views/test_index.py

Fix tests querying the header navigation
- tests/app/test_navigation.py

tests/app/main/views/test_index.py

@@ -172,10 +172,8 @@ def test_css_is_served_from_correct_path(client_request):
         page.select('link[rel=stylesheet]')
     ):
         assert link['href'].startswith([
-            'https://static.example.com/stylesheets/govuk-template.css?',
-            'https://static.example.com/stylesheets/govuk-template-print.css?',
-            'https://static.example.com/stylesheets/fonts.css?',
             'https://static.example.com/stylesheets/main.css?',
+            'https://static.example.com/stylesheets/print.css?',
         ][index])