Sets the function that runs when a repeated item is removed.
Use the onItemRemoved() function for code you want to run when
repeated items are removed. The callback is triggered when you remove
items by setting the value of the data property to an array
in which some of the existing item IDs are no longer present or when items
are removed based on a dataset that is connected to the repeater.
Note: The onItemRemoved() callback function is not called when the static
repeated items that were set in the Editor are removed.
handler(itemData: object): void The name of the function or
the function expression to run when the item is removed.