ROADMAP: Remove digest/hashing target

Most of this has spun off with [1], and I haven't heard of anyone
talking about verifying the on-disk filesystem in a while.  My
personal take is on-disk verification doesn't add much over serialized
verification unless you have a local attacker (or unreliable disk),
and you'll need some careful threat modeling if you want to do
anything productive about the local attacker case.  For some more
on-disk verification discussion, see the thread starting with [2].

[1]: https://github.com/opencontainers/image-spec
[2]: https://groups.google.com/a/opencontainers.org/d/msg/dev/xo4SQ92aWJ8/NHpSQ19KCAAJ
     Subject: OCI Bundle Digests Summary
     Date: Wed, 14 Oct 2015 17:09:15 +0000
     Message-ID: <CAD2oYtN-9yLLhG_STO3F1h58Bn5QovK+u3wOBa=t+7TQi-hP1Q@mail.gmail.com>

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

ROADMAP.md

@@ -10,13 +10,6 @@ Listed topics may defer to the [project wiki](https://github.com/opencontainers/
 
 ## 1.0
 
-### Digest and Hashing
-
-A bundle is designed to be moved between hosts.
-Although OCI doesn't define a transport method we should have a cryptographic digest of the on-disk bundle that can be used to verify that a bundle is not corrupted and in an expected configuration.
-
-*Owner:* philips
-
 ### Define Container Lifecycle
 
 Containers have a lifecycle and being able to identify and document the lifecycle of a container is very helpful for implementations of the spec.