Do not consider attributes using the :unless option as required

Remove some of the factories introduced in commit 66334b5 as now we do
not need them anymore.

Co-Authored-By: Javi Martín <35156+javierm@users.noreply.github.com>

spec/models/proposal_spec.rb

@@ -7,7 +7,7 @@ describe Proposal do
     it_behaves_like "has_public_author"
     it_behaves_like "notifiable"
     it_behaves_like "map validations"
-    it_behaves_like "globalizable", :retired_proposal
+    it_behaves_like "globalizable", :proposal
     it_behaves_like "sanitizable"
     it_behaves_like "acts as paranoid", :proposal
   end