Remove overriding of copy_elements parameter

Prevent unexpected behaviour of the API.
Actually raise `RequestParameterInvalidException` exception if this
conflicts with `copy_required` (i.e. dbkey not None).

lib/galaxy/webapps/galaxy/services/history_contents.py

@@ -1269,9 +1269,9 @@ def __create_dataset_collection(
                 raise exceptions.RequestParameterMissingException("'content' id of target to copy is missing")
             dbkey = payload.dbkey
             copy_required = dbkey is not None
-            copy_elements = payload.copy_elements or copy_required
+            copy_elements = payload.copy_elements
             if copy_required and not copy_elements:
-                raise exceptions.RequestParameterMissingException(
+                raise exceptions.RequestParameterInvalidException(
                     "copy_elements passed as 'false' but it is required to change specified attributes"
                 )
             dataset_instance_attributes = {}