The CustomMenuItems settings have been replaced by the CreateNewAndSearchManager setting since the May 2016 update. If your Flex site has a later update than May 2016 you may remove these Settings.
The CustomMenuItems settings manage what actions are available from the Custom List Menus, for Quick Search results and for the Search & Create New Item Wizard.
From any List View, the hyperlinked field will contain a drop-down menu (this is the Custom Menu):
Setting Name: [ListName]CustomMenuItems
Setting Value: [Listname]|[Menu text]|[Image File name] each on a separate line
Removing Setting Value items from the CustomMenuItems Setting will remove those actions from the Custom Menus, Quick Search Result pane and Search & Create New Wizard.
The following screenshot shows Quick Search Results – the Action Icons that appear are controlled by the Custom Menu Items Setting: