Remove unecessary CE property from board data

app/helpers/boards_helper.rb

@@ -10,7 +10,6 @@ module BoardsHelper
       boards_endpoint: @boards_endpoint,
       lists_endpoint: board_lists_url(board),
       board_id: board.id,
-      board_milestone_title: board&.milestone&.title,
       disabled: "#{!can?(current_user, :admin_list, current_board_parent)}",
       issue_link_base: build_issue_link_base,
       root_path: root_path,

ee/app/helpers/ee/boards_helper.rb

@@ -2,7 +2,13 @@ module EE
   module BoardsHelper
     def board_data
       parent = @group || @project
-      super.merge(focus_mode_available: parent.feature_available?(:issue_board_focus_mode).to_s)
+
+      data = {
+        board_milestone_title: board&.milestone&.title,
+        focus_mode_available: parent.feature_available?(:issue_board_focus_mode).to_s
+      }
+
+      super.merge(data)
     end
 
     def build_issue_link_base