Remove milestones_in_roadmap feature flag

ee/app/assets/javascripts/roadmap/components/roadmap_shell.vue

@@ -40,16 +40,14 @@ export default {
     },
   },
   data() {
-    const milestonesInRoadmap = gon.features && gon.features.milestonesInRoadmap;
     return {
       timeframeStartOffset: 0,
-      milestonesInRoadmap,
     };
   },
   computed: {
     ...mapState(['defaultInnerHeight']),
     displayMilestones() {
-      return this.milestonesInRoadmap && this.milestones.length !== 0;
+      return Boolean(this.milestones.length);
     },
   },
   mounted() {

ee/app/controllers/groups/roadmap_controller.rb

@@ -11,7 +11,6 @@ module Groups
     before_action :persist_roadmap_layout, only: [:show]
     before_action do
       push_frontend_feature_flag(:roadmap_buffered_rendering, @group)
-      push_frontend_feature_flag(:milestones_in_roadmap, @group)
     end
 
     # show roadmap for a group