Remove case study from canonicalisation test

* This logic doesn’t need to be handled by Whitehall
* Note: government-frontend doesn’t do this redirect:
https://www.gov.uk/government/case-studies/bis-criminal-prosecutions?loc
ale=en

test/integration/document_locale_param_canonicalisation_test.rb

@@ -10,14 +10,7 @@ def with_locale_param(path, locale)
     u.to_s
   end
 
-  document_types_with_no_index = %w(case_study)
-  normal_document_types = [
-    "world_location_news_article",
-    "publication",
-    "consultation",
-  ]
-
-  (document_types_with_no_index + normal_document_types).each do |doc_type|
+  %w{world_location_news_article publication consultation}.each do |doc_type|
     test "visiting a #{doc_type} with a spurious locale=en param will redirect to remove it" do
       canonical_path = send("#{doc_type}_path", "a-#{doc_type}")
       extra_path = with_locale_param(canonical_path, 'en')