Implementation collapse: Drop namedRef
Implementation collapse: Drop namedRef

(This could have been done a few commits ago.)

Now that namedRef merely wraps a distreference.Named, adding no
functionality, just use a distreference.Named directly.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

masters-of-cats/image,containers/image,containers/image