Fix container pid.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/process/utils.go

@@ -39,8 +39,6 @@ import (
 const (
 	// RuncRoot is the path to the root runc state directory
 	RuncRoot = "/run/containerd/runc"
-	// StoppedPID is the pid assigned after a container has run and stopped
-	StoppedPID = -1
 	// InitPidFile name of the file that contains the init pid
 	InitPidFile = "init.pid"
 )
@@ -57,12 +55,6 @@ func (s *safePid) get() int {
 	return s.pid
 }
 
-func (s *safePid) set(pid int) {
-	s.Lock()
-	s.pid = pid
-	s.Unlock()
-}
-
 type atomicBool int32
 
 func (ab *atomicBool) set(b bool) {