Remove design_management_flag feature flag

https://gitlab.com/gitlab-org/gitlab/issues/13709

ee/app/models/ee/project.rb

@@ -663,12 +663,7 @@ module EE
         # hashed storage requirement for existing design management projects.
         # See https://gitlab.com/gitlab-org/gitlab/issues/13428#note_238729038
         (hashed_storage?(:repository) || ::Feature.disabled?(:design_management_require_hashed_storage, self, default_enabled: true)) &&
-        # Check both feature availability on the license, as well as the feature
-        # flag, because we don't want to enable design_management by default on
-        # on prem installs yet.
-        # See https://gitlab.com/gitlab-org/gitlab/issues/13709
-        feature_available?(:design_management) &&
-        ::Feature.enabled?(:design_management_flag, self, default_enabled: true)
+        feature_available?(:design_management)
     end
 
     def design_repository

ee/changelogs/unreleased/13709-remove-design-management-flag.yml

+---
+title: Remove the design_management_flag feature flag from the codebase. The feature
+  flag toggles the Design Management feature, and has been enabled by default since
+  12.2.
+merge_request: 20883
+author:
+type: other

ee/spec/features/issues/issues_tabs_spec.rb

@@ -9,8 +9,6 @@ describe 'Issue page tabs', :js do
 
   describe 'discussions tab counter' do
     before do
-      stub_licensed_features(design_management: true)
-      stub_feature_flags(design_management_flag: true)
       allow(Ability).to receive(:allowed?) { true }
     end
 

ee/spec/models/project_spec.rb

@@ -1903,20 +1903,19 @@ describe Project do
   describe '#design_management_enabled?' do
     let(:project) { build(:project) }
 
-    where(:feature_enabled, :license_enabled, :lfs_enabled, :hashed_storage_enabled, :hash_storage_required, :expectation) do
-      false | false | false | false | false | false
-      true  | false | false | false | false | false
-      true  | true  | false | false | false | false
-      true  | true  | true  | false | false | true
-      true  | true  | true  | false | true  | false
-      true  | true  | true  | true  | false | true
-      true  | true  | true  | true  | true  | true
+    where(:license_enabled, :lfs_enabled, :hashed_storage_enabled, :hash_storage_required, :expectation) do
+      false | false | false | false | false
+      true  | false | false | false | false
+      true  | true  | false | false | true
+      true  | true  | false | true  | false
+      true  | true  | true  | false | true
+      true  | true  | true  | true  | true
     end
 
     with_them do
       before do
         stub_licensed_features(design_management: license_enabled)
-        stub_feature_flags(design_management_flag: feature_enabled, design_management_require_hashed_storage: hash_storage_required)
+        stub_feature_flags(design_management_require_hashed_storage: hash_storage_required)
         expect(project).to receive(:lfs_enabled?).and_return(lfs_enabled)
         allow(project).to receive(:hashed_storage?).with(:repository).and_return(hashed_storage_enabled)
       end

ee/spec/policies/design_management/design_policy_spec.rb

@@ -99,20 +99,9 @@ describe DesignManagement::DesignPolicy do
     it { is_expected.to be_disallowed(:create_design, :destroy_design) }
   end
 
-  context "when the feature flag is off" do
-    before do
-      stub_licensed_features(design_management: true)
-      stub_feature_flags(design_management_flag: false)
-      allow(Gitlab.config.lfs).to receive(:enabled).and_return(true)
-    end
-
-    it_behaves_like "design abilities not available"
-  end
-
   context "when the license does not include the feature" do
     before do
       stub_licensed_features(design_management: false)
-      stub_feature_flags(design_management_flag: true)
       allow(Gitlab.config.lfs).to receive(:enabled).and_return(true)
     end
 
@@ -122,7 +111,6 @@ describe DesignManagement::DesignPolicy do
   context "when LFS is not enabled" do
     before do
       stub_licensed_features(design_management: true)
-      stub_feature_flags(design_management_flag: true)
       allow(Gitlab.config.lfs).to receive(:enabled).and_return(false)
     end