sys: un-export runningPrivileged(), remove runningUnprivileged()

These are currently only used inside this package, so we might
as well un-export them until we need them elsewhere.

Also updated SetOOMScore() to first check for privileged; check for privileged
looks to be the "faster" path, and checking it first could (in case of non-
privileged) save having to read and parse /proc/self/uid_map.

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

sys/mount_linux_test.go

@@ -32,7 +32,7 @@ import (
 type fMountatCaseFunc func(t *testing.T, root string)
 
 func TestFMountat(t *testing.T) {
-	if RunningUnprivileged() {
+	if !runningPrivileged() {
 		t.Skip("Needs to be run as root")
 		return
 	}