If you delete an existing element in a schema file and reload the schema file, stale aliases are generated. You can delete these stale aliases from the process composer DC provided they are not being used in the rule.
Project Explorer view, expand the
Process Modeling node and the
Rules and Functions node and double click the Ruleset node.
In the Ruleset Aliases Editor, choose the
Aliases tab and choose the Stale Aliases as shown below: