remove obsolete favicon related spec

the favicon variations don't need to be tested on the entity anymore, as
they are A) tested in the dedicated `Gitlab::Favicon` and B) they are
created on the client (i.e. the overlays are always the same for all
base favicon variants).

spec/serializers/status_entity_spec.rb

@@ -20,15 +20,5 @@ describe StatusEntity do
       expect(subject).to include :has_details, :details_path
       expect(subject[:favicon]).to match_asset_path('/assets/ci_favicons/favicon_status_success.png')
     end
-
-    it 'contains a dev namespaced favicon if dev env' do
-      allow(Rails.env).to receive(:development?) { true }
-      expect(entity.as_json[:favicon]).to match_asset_path('/assets/ci_favicons/favicon_status_success.png')
-    end
-
-    it 'contains a canary namespaced favicon if canary env' do
-      stub_env('CANARY', 'true')
-      expect(entity.as_json[:favicon]).to match_asset_path('/assets/ci_favicons/canary/favicon_status_success.png')
-    end
   end
 end