Remove WithSubrepaer which isn't used

This option was unused and was trying to set a field that doesn't exist
anymore.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

components/engine/libcontainerd/remote_daemon_options_linux.go

@@ -16,19 +16,3 @@ func (o oomScore) Apply(r Remote) error {
 	}
 	return fmt.Errorf("WithOOMScore option not supported for this remote")
 }
-
-// WithSubreaper sets whether containerd should register itself as a
-// subreaper
-func WithSubreaper(reap bool) RemoteOption {
-	return subreaper(reap)
-}
-
-type subreaper bool
-
-func (s subreaper) Apply(r Remote) error {
-	if remote, ok := r.(*remote); ok {
-		remote.NoSubreaper = !bool(s)
-		return nil
-	}
-	return fmt.Errorf("WithSubreaper option not supported for this remote")
-}