libct/cg: remove retry on EINTR in

Commit f34eb2c00 introduced a workaround to retry on EINTR due to changes in Go 1.14.
It was fixed in Go 1.15 [1], meaning a custom retry loop is no longer
necessary.

Keep the test case to avoid future regressions.

[1] https://github.com/golang/go/issues/38033

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/file.go

@@ -49,24 +49,13 @@ func WriteFile(dir, file, data string) error {
 		return err
 	}
 	defer fd.Close()
-	if err := retryingWriteFile(fd, data); err != nil {
+	if _, err := fd.WriteString(data); err != nil {
 		// Having data in the error message helps in debugging.
 		return fmt.Errorf("failed to write %q: %w", data, err)
 	}
 	return nil
 }
 
-func retryingWriteFile(fd *os.File, data string) error {
-	for {
-		_, err := fd.Write([]byte(data))
-		if errors.Is(err, unix.EINTR) {
-			logrus.Infof("interrupted while writing %s to %s", data, fd.Name())
-			continue
-		}
-		return err
-	}
-}
-
 const (
 	cgroupfsDir    = "/sys/fs/cgroup"
 	cgroupfsPrefix = cgroupfsDir + "/"