Remove optimized_timebox_queries feature flag

- Remove relevant code
- Update relevant specs

Changelog: other

app/models/concerns/timebox.rb

@@ -72,11 +72,7 @@ module Timebox
       groups = groups.compact if groups.is_a? Array
       groups = [] if groups.nil?
 
-      if Feature.enabled?(:optimized_timebox_queries, default_enabled: true)
-        from_union([where(project_id: projects), where(group_id: groups)], remove_duplicates: false)
-      else
-        where(project_id: projects).or(where(group_id: groups))
-      end
+      from_union([where(project_id: projects), where(group_id: groups)], remove_duplicates: false)
     end
 
     # A timebox is within the timeframe (start_date, end_date) if it overlaps

changelogs/unreleased/mr-34043-remove-optimized_timebox_queries-ff.yml

+---
+title: Remove optimized_timebox_queries feature flag
+merge_request: 60326
+author:
+type: other

config/feature_flags/development/optimized_timebox_queries.yml

----
-name: optimized_timebox_queries
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/32953
-rollout_issue_url:  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34043
-milestone: '13.1'
-type: development
-group: group::project management
-default_enabled: true

spec/models/milestone_spec.rb

@@ -293,21 +293,7 @@ RSpec.describe Milestone do
     end
   end
 
-  context 'when `optimized_timebox_queries` feature flag is enabled' do
-    before do
-      stub_feature_flags(optimized_timebox_queries: true)
-    end
-
-    it_behaves_like '#for_projects_and_groups'
-  end
-
-  context 'when `optimized_timebox_queries` feature flag is disabled' do
-    before do
-      stub_feature_flags(optimized_timebox_queries: false)
-    end
-
-    it_behaves_like '#for_projects_and_groups'
-  end
+  it_behaves_like '#for_projects_and_groups'
 
   describe '.upcoming_ids' do
     let(:group_1) { create(:group) }