libct/cg: rm GetInitCgroup[Path]

These functions were added in ancient times, facilitating the
docker-in-docker case when cgroup namespace was not available.

As pointed out in commit 2b28b3c276, using init 1 cgroup is not
correct because it won't work in case of host PID namespace.

The last user of GetInitCgroup was removed by commit
54e20217a8. GetInitCgroupPath was never used
as far as I can see, nor was I able to find any external users.

Remove both functions. Modify the comment in libct/cg/fs.subsysPath
to not refer to GetInitCgroupPath.

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

libcontainer/cgroups/fs/paths.go

@@ -164,9 +164,8 @@ func subsysPath(root, inner, subsystem string) (string, error) {
 		return filepath.Join(root, filepath.Base(mnt), inner), nil
 	}
 
-	// Use GetOwnCgroupPath instead of GetInitCgroupPath, because the creating
-	// process could in container and shared pid namespace with host, and
-	// /proc/1/cgroup could point to whole other world of cgroups.
+	// Use GetOwnCgroupPath for dind-like cases, when cgroupns is not
+	// available. This is ugly.
 	parentPath, err := cgroups.GetOwnCgroupPath(subsystem)
 	if err != nil {
 		return "", err

libcontainer/cgroups/v1_utils.go

@@ -236,27 +236,6 @@ func GetOwnCgroupPath(subsystem string) (string, error) {
 	return getCgroupPathHelper(subsystem, cgroup)
 }
 
-func GetInitCgroup(subsystem string) (string, error) {
-	if IsCgroup2UnifiedMode() {
-		return "", errUnified
-	}
-	cgroups, err := ParseCgroupFile("/proc/1/cgroup")
-	if err != nil {
-		return "", err
-	}
-
-	return getControllerPath(subsystem, cgroups)
-}
-
-func GetInitCgroupPath(subsystem string) (string, error) {
-	cgroup, err := GetInitCgroup(subsystem)
-	if err != nil {
-		return "", err
-	}
-
-	return getCgroupPathHelper(subsystem, cgroup)
-}
-
 func getCgroupPathHelper(subsystem, cgroup string) (string, error) {
 	mnt, root, err := FindCgroupMountpointAndRoot("", subsystem)
 	if err != nil {