Remove the 'Add' list banner button from a related list
This button mysteriously became available after installing the Problem Management Best Practice - Madrid plugins (it is actually a good feature and worth retaining, but below shows steps to remove if it's not to be present)
in this case, the conditions of the UI action reference script include BulkAddIncidents.canShowAddButton which does a lookup on a sys property, which appears to have become created with activation of the best practice plugin
Hence the following seemed to do the trick and remove the 'add' button
although keeping it allows for some nice functionality!