Refactor AttributeCleaner` for readability

lib/gitlab/import_export/attribute_cleaner.rb

@@ -24,14 +24,9 @@ module Gitlab
       private
       def prohibited_key?(key)
-        return false if allowed_reference?(key)
-        return true if 'cached_markdown_version'.equal?(key)
-
-        prohibited_suffixes = %w(_id _html)
-        prohibited_suffixes.any? do |suffix|
-          true if key.end_with?(suffix)
-        end
+        return false if permitted_key?(key)
+        'cached_markdown_version' == key || PROHIBITED_SUFFIXES.any? {|suffix| key.end_with?(suffix)}
       end
       def allowed_reference?(key)