Remove unused `IssuesHelper#bulk_update_milestone_options`

Its last usage has been removed at 2e3c082f.

app/helpers/issues_helper.rb

@@ -47,13 +47,6 @@ module IssuesHelper
     end
   end
 
-  def bulk_update_milestone_options
-    milestones = @project.milestones.active.reorder(due_date: :asc, title: :asc).to_a
-    milestones.unshift(Milestone::None)
-
-    options_from_collection_for_select(milestones, 'id', 'title', params[:milestone_id])
-  end
-
   def milestone_options(object)
     milestones = object.project.milestones.active.reorder(due_date: :asc, title: :asc).to_a
     milestones.unshift(object.milestone) if object.milestone.present? && object.milestone.closed?