fix: linter issue

megacheck, gosimple and unused has been deprecated and subsumed by
staticcheck. And staticcheck also has been upgraded. we need to update
code for the linter issue.

close: #2945

Signed-off-by: Wei Fu <fuweid89@gmail.com>

runtime/v2/shim/shim_unix.go

@@ -76,9 +76,9 @@ func serveListener(path string) (net.Listener, error) {
 
 func handleSignals(logger *logrus.Entry, signals chan os.Signal) error {
 	logger.Info("starting signal loop")
+
 	for {
-		select {
-		case s := <-signals:
+		for s := range signals {
 			switch s {
 			case unix.SIGCHLD:
 				if err := Reap(); err != nil {

runtime/v2/shim/shim_windows.go

@@ -108,12 +108,11 @@ func serveListener(path string) (net.Listener, error) {
 
 func handleSignals(logger *logrus.Entry, signals chan os.Signal) error {
 	logger.Info("starting signal loop")
+
 	for {
-		select {
-		case s := <-signals:
+		for s := range signals {
 			switch s {
 			case os.Interrupt:
-				break
 			}
 		}
 	}

runtime/v2/shim/util_windows.go

@@ -54,7 +54,7 @@ func AnonDialer(address string, timeout time.Duration) (net.Conn, error) {
 	timedOutError := errors.Errorf("timed out waiting for npipe %s", address)
 	start := time.Now()
 	for {
-		remaining := timeout - time.Now().Sub(start)
+		remaining := timeout - time.Since(start)
 		if remaining <= 0 {
 			lastError = timedOutError
 			break
@@ -71,7 +71,7 @@ func AnonDialer(address string, timeout time.Duration) (net.Conn, error) {
 		// serve it within 5 seconds. We use the passed in timeout for the
 		// `DialPipe` timeout if the pipe exists however to give the pipe time
 		// to `Accept` the connection.
-		if time.Now().Sub(start) >= 5*time.Second {
+		if time.Since(start) >= 5*time.Second {
 			lastError = timedOutError
 			break
 		}