Remove duplicate file

This is already moved to
ee/lib/gitlab/analytics/cycle_analytics/summary/stage_time_summary.rb

ee/lib/gitlab/analytics/cycle_analytics/summary/group/stage_time_summary.rb

-# frozen_string_literal: true
-
-module Gitlab
-  module Analytics
-    module CycleAnalytics
-      module Summary
-        class StageTimeSummary
-          attr_reader :stage, :current_user, :options
-
-          def initialize(stage, options:)
-            @stage = stage
-            @current_user = options[:current_user]
-            @options = options
-          end
-
-          def data
-            [lead_time, cycle_time]
-          end
-
-          private
-
-          def lead_time
-            serialize(
-              Summary::LeadTime.new(
-                stage: stage, current_user: current_user, options: options
-              ),
-              with_unit: true
-            )
-          end
-
-          def cycle_time
-            serialize(
-              Summary::CycleTime.new(
-                stage: stage, current_user: current_user, options: options
-              ),
-              with_unit: true
-            )
-          end
-
-          def serialize(summary_object, with_unit: false)
-            AnalyticsSummarySerializer.new.represent(
-              summary_object, with_unit: with_unit)
-          end
-        end
-      end
-    end
-  end
-end