handler: remove unused SinkMappingFunc

cmd/config_job_source.go

@@ -104,7 +104,6 @@ outer:
 			handler := Handler{
 				Logger:  log,
 				PullACL: j.Datasets,
-				// TODO should set SinkMapping here? no, but check Handler impl
 			}
 
 			// handle connection

cmd/handler.go

@@ -34,7 +34,6 @@ type IncrementalTransferRequest struct {
 type Handler struct {
 	Logger  Logger
 	PullACL zfs.DatasetFilter
-	SinkMappingFunc func(clientIdentity string) (mapping DatasetMapping, err error)
 }
 
 func registerEndpoints(server rpc.RPCServer, handler Handler) (err error) {