Remove duplicate feature flag

This MR removes a feature flag instantiated twice
and also remove the changelog for the same

ee/app/controllers/ee/projects/pipelines_controller.rb

@@ -12,7 +12,6 @@ module EE
 
       def security
         if pipeline.expose_security_dashboard?
-          push_frontend_feature_flag(:pipelines_security_report_summary, default_enabled: false)
           render_show
         else
           redirect_to pipeline_path(pipeline)

ee/changelogs/unreleased/djadmin-pipeline-dast-modal.yml

----
-title: Implement DAST Modal for Pipeline View
-merge_request: 38267
-author:
-type: added