Enable linear GroupTree ancestors queries

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

Changelog: added

app/controllers/concerns/group_tree.rb

@@ -38,13 +38,7 @@ module GroupTree
     #
     # Pagination needs to be applied before loading the ancestors to
     # make sure ancestors are not cut off by pagination.
-    filtered_groups_relation = Group.where(id: filtered_groups.select(:id))
-
-    if Feature.enabled?(:linear_group_tree_ancestor_scopes, current_user, default_enabled: :yaml)
-      filtered_groups_relation.self_and_ancestors
-    else
-      Gitlab::ObjectHierarchy.new(filtered_groups_relation).base_and_ancestors
-    end
+    Group.where(id: filtered_groups.select(:id)).self_and_ancestors
   end
   # rubocop: enable CodeReuse/ActiveRecord
 end

config/feature_flags/development/linear_group_tree_ancestor_scopes.yml

----
-name: linear_group_tree_ancestor_scopes
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/70503
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341117
-milestone: '14.4'
-type: development
-group: group::access
-default_enabled: false

spec/controllers/concerns/group_tree_spec.rb

@@ -102,13 +102,5 @@ RSpec.describe GroupTree do
     end
 
     it_behaves_like 'returns filtered groups'
-
-    context 'when feature flag :linear_group_tree_ancestor_scopes is disabled' do
-      before do
-        stub_feature_flags(linear_group_tree_ancestor_scopes: false)
-      end
-
-      it_behaves_like 'returns filtered groups'
-    end
   end
 end