Remove useless named return value

This cleans up the useless named return value stopCh at
SetupSignalHandler().

staging/src/k8s.io/apiserver/pkg/server/signal.go

@@ -26,7 +26,7 @@ var onlyOneSignalHandler = make(chan struct{})
 // SetupSignalHandler registered for SIGTERM and SIGINT. A stop channel is returned
 // which is closed on one of these signals. If a second signal is caught, the program
 // is terminated with exit code 1.
-func SetupSignalHandler() (stopCh <-chan struct{}) {
+func SetupSignalHandler() <-chan struct{} {
 	close(onlyOneSignalHandler) // panics when called twice
 
 	stop := make(chan struct{})