Remove render_dashboard_gold_trial feature flag

This flag was added as `default_enabled: true`, and we haven't needed to
disable it in several months.

ee/app/helpers/ee/user_callouts_helper.rb

@@ -55,7 +55,6 @@ module EE
     def render_dashboard_gold_trial(user)
       return unless show_gold_trial?(user, GOLD_TRIAL) &&
           user_default_dashboard?(user) &&
-          ::Feature.enabled?(:render_dashboard_gold_trial, default_enabled: true) &&
           !user.owns_paid_namespace? &&
           user.any_namespace_without_trial?
 

ee/config/feature_flags/development/render_dashboard_gold_trial.yml

----
-name: render_dashboard_gold_trial
-introduced_by_url: 
-rollout_issue_url: 
-group: 
-type: development
-default_enabled: true

ee/spec/helpers/ee/user_callouts_helper_spec.rb

@@ -217,22 +217,6 @@ RSpec.describe EE::UserCalloutsHelper do
         helper.render_dashboard_gold_trial(user)
       end
     end
-
-    context 'when render_dashboard_gold_trial feature is disabled' do
-      before do
-        stub_feature_flags(render_dashboard_gold_trial: false)
-
-        allow(helper).to receive(:show_gold_trial?).and_return(true)
-        allow(helper).to receive(:user_default_dashboard?).and_return(true)
-        allow(helper).to receive(:has_some_namespaces_with_no_trials?).and_return(true)
-      end
-
-      it 'does not render' do
-        expect(helper).not_to receive(:render)
-
-        helper.render_dashboard_gold_trial(user)
-      end
-    end
   end
 
   describe '#render_billings_gold_trial' do