mnt: Don't include fake root entry in every mnt tree

This entry is only required if we have it, i.e. -- at restore stage
in the tree we _built_. All other cases, in particular, local tree
collection on restore, do not need such.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Andrew Vagin <avagin@odin.com>