pkg/userns: deprecate and migrate to github.com/moby/sys/user/userns

The userns package in libcontainer was integrated into the moby/sys/user
module at commit [3778ae603c706494fd1e2c2faf83b406e38d687d][1].

This patch deprecates the containerd fork of that package, and adds it as
an alias for the moby/sys/user/userns package.

[1]: 3778ae603c

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/archive/tar_unix.go

@@ -27,10 +27,11 @@ import (
 	"strings"
 	"syscall"
 
-	"github.com/containerd/containerd/v2/pkg/userns"
+	"github.com/moby/sys/user/userns"
+	"golang.org/x/sys/unix"
+
 	"github.com/containerd/continuity/fs"
 	"github.com/containerd/continuity/sysx"
-	"golang.org/x/sys/unix"
 )
 
 func chmodTarEntry(perm os.FileMode) os.FileMode {