Enable linear ancestors for groups

In this commit, we're removing the feature flag
`linear_group_ancestor_scopes` to allow group queries
using linear queries.

Changelog: added

app/models/group.rb

@@ -194,13 +194,8 @@ class Group < Namespace
     def ids_with_disabled_email(groups)
       inner_groups = Group.where('id = namespaces_with_emails_disabled.id')
 
-      inner_ancestors = if Feature.enabled?(:linear_group_ancestor_scopes, default_enabled: :yaml)
-                          inner_groups.self_and_ancestors
-                        else
-                          Gitlab::ObjectHierarchy.new(inner_groups).base_and_ancestors
-                        end
-
-      inner_query = inner_ancestors
+      inner_query = inner_groups
+        .self_and_ancestors
         .where(emails_disabled: true)
         .select('1')
         .limit(1)

config/feature_flags/development/linear_group_ancestor_scopes.yml

----
-name: linear_group_ancestor_scopes
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/70495
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341115
-milestone: '14.4'
-type: development
-group: group::access
-default_enabled: false

spec/models/group_spec.rb

@@ -2648,14 +2648,6 @@ RSpec.describe Group do
     end
 
     it_behaves_like 'returns namespaces with disabled email'
-
-    context 'when feature flag :linear_group_ancestor_scopes is disabled' do
-      before do
-        stub_feature_flags(linear_group_ancestor_scopes: false)
-      end
-
-      it_behaves_like 'returns namespaces with disabled email'
-    end
   end
 
   describe '.timelogs' do