Remove subscribable_subscription_banner flag

Removes the `subscribable_subscription_banner` feature
flag

Changelog: other
EE: true

ee/app/helpers/ee/subscribable_banner_helper.rb

@@ -73,9 +73,7 @@ module EE
     end
 
     def display_subscription_banner?
-      @display_subscription_banner &&
-        ::Gitlab::CurrentSettings.should_check_namespace_plan? &&
-        ::Feature.enabled?(:subscribable_subscription_banner, default_enabled: false)
+      @display_subscription_banner && ::Gitlab::CurrentSettings.should_check_namespace_plan?
     end
   end
 end

ee/config/feature_flags/development/subscribable_subscription_banner.yml

----
-name: subscribable_subscription_banner
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/31497
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/230858
-milestone: '13.1'
-type: development
-group: group::utilization
-default_enabled: false

ee/spec/helpers/ee/subscribable_banner_helper_spec.rb

@@ -107,11 +107,6 @@ RSpec.describe EE::SubscribableBannerHelper do
 
     let(:message) { double(:message) }
 
-    context 'when subscribable_subscription_banner feature flag is enabled' do
-      before do
-        stub_feature_flags(subscribable_subscription_banner: true)
-      end
-
     context 'when instance variable true' do
       before do
         assign(:display_subscription_banner, true)
@@ -212,20 +207,6 @@ RSpec.describe EE::SubscribableBannerHelper do
     end
   end
 
-    context 'when subscribable_subscription_banner feature flag is disabled' do
-      before do
-        stub_feature_flags(subscribable_subscription_banner: false)
-        assign(:display_subscription_banner, true)
-        allow(::Gitlab::CurrentSettings).to receive(:should_check_namespace_plan?).and_return(true)
-      end
-
-      it 'returns the license message' do
-        expect(helper).to receive(:license_message).and_return(message)
-        expect(subject).to eq(message)
-      end
-    end
-  end
-
   describe '#display_subscription_banner!' do
     it 'sets @display_subscription_banner to true' do
       expect(helper.instance_variable_get(:@display_subscription_banner)).to be nil