update to use deduplication for invalid cluster names

Co-authored-by: Zac Bergquist <[email protected]>

lib/services/access_request.go

@@ -120,13 +120,8 @@ func ValidateAccessRequestClusterNames(cg ClusterGetter, ar types.AccessRequest)
 		}
 	}
 	if len(invalidClusters) > 0 {
-		// Multiple resources are requestable with the same or different cluster names.
-		// Prior to showing the error message, sort the list and remove duplicates so
-		// the same cluster name isn't repeated.
-		slices.Sort(invalidClusters)
-		invalidClusters = slices.Compact(invalidClusters)
 		return trace.NotFound("access request contains invalid or unknown cluster names: %v",
-			strings.Join(invalidClusters, ", "))
+			strings.Join(utils.Deduplicate(invalidClusters), ", "))
 	}
 	return nil
 }