Duplicating an application containing a table with a field of type=link can raise a KeyError if the page was deleted.

Corresponds to Sentry issue 5428353684.

• Create a page with a table element.
• Give the table a CollectionField of type=link.
• Point the field to a different page (pageB)
• Delete pageB.
• Duplicate the application.
• A KeyError is raised when we try and pluck the page ID out of id_mapping["builder_pages"] in deserialize_property.