Fix use of removed function isUniqueListKey

Function was removed in eb647434363c4b but one caller was still left,
which caused VE to throw a JS error when opening the reference dialog
to insert a new reference.

Change-Id: I827381bfe3bdeecdbaa1fba55a09b3e8e03575a6
Merge "Fix use of removed function isUniqueListKey"