Revert "Merge pull request 101888 from kolyshkin/update-runc-rc94"

This reverts commit b1b06fe0a4, reversing
changes made to 382a33986b.

vendor/github.com/opencontainers/runc/libcontainer/userns/userns_linux.go

@@ -1,37 +0,0 @@
-package userns
-
-import (
-	"sync"
-
-	"github.com/opencontainers/runc/libcontainer/user"
-)
-
-var (
-	inUserNS bool
-	nsOnce   sync.Once
-)
-
-// runningInUserNS detects whether we are currently running in a user namespace.
-// Originally copied from github.com/lxc/lxd/shared/util.go
-func runningInUserNS() bool {
-	nsOnce.Do(func() {
-		uidmap, err := user.CurrentProcessUIDMap()
-		if err != nil {
-			// This kernel-provided file only exists if user namespaces are supported
-			return
-		}
-		inUserNS = uidMapInUserNS(uidmap)
-	})
-	return inUserNS
-}
-
-func uidMapInUserNS(uidmap []user.IDMap) bool {
-	/*
-	 * We assume we are in the initial user namespace if we have a full
-	 * range - 4294967295 uids starting at uid 0.
-	 */
-	if len(uidmap) == 1 && uidmap[0].ID == 0 && uidmap[0].ParentID == 0 && uidmap[0].Count == 4294967295 {
-		return false
-	}
-	return true
-}