Enable shared runners on descendants

Just remove the FF introduced in the previous commit

See more in https://gitlab.com/gitlab-org/gitlab/-/issues/299823

Changelog: added

app/services/groups/update_shared_runners_service.rb

@@ -54,8 +54,6 @@ def set_shared_runners_enabled!(enabled)
         shared_runners_enabled: enabled,
         allow_descendants_override_disabled_shared_runners: false)
 
-      return if enabled && Feature.disabled?(:enable_shared_runners_for_descendants, group)
-
       group_ids = group.descendants
       unless group_ids.empty?
         Group.by_id(group_ids).update_all(

config/feature_flags/development/enable_shared_runners_for_descendants.yml

----
-name: enable_shared_runners_for_descendants
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/124728
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/416379
-milestone: '16.2'
-type: development
-group: group::runner
-default_enabled: false

doc/ci/runners/runners_scope.md

@@ -139,10 +139,6 @@ To disable shared runners for a group:
 1. Optional. To allow shared runners to be enabled for individual projects or subgroups,
    select **Allow projects and subgroups to override the group setting**.
 
-NOTE:
-If you re-enable the shared runners for a group after you disable them, a user with the
-Owner or Maintainer role must manually change this setting for each project subgroup or project.
-
 ### How shared runners pick jobs
 
 Shared runners process jobs by using a fair usage queue. This queue prevents

spec/services/groups/update_shared_runners_service_spec.rb

@@ -67,22 +67,6 @@
               .and change { sub_group.shared_runners_enabled }.from(false).to(true)
               .and change { project.shared_runners_enabled }.from(false).to(true)
           end
-
-          context 'when enable_shared_runners_for_descendants feature flag is disabled' do
-            before do
-              stub_feature_flags(enable_shared_runners_for_descendants: false)
-            end
-
-            it 'enables shared Runners only for itself' do
-              expect do
-                expect(subject[:status]).to eq(:success)
-
-                reload_models(group, sub_group, project)
-              end.to change { group.shared_runners_enabled }.from(false).to(true)
-                .and not_change { sub_group.shared_runners_enabled }.from(false)
-                .and not_change { project.shared_runners_enabled }.from(false)
-            end
-          end
         end
 
         context 'when group has pending builds' do