removal of /run/opencontainer/containers (fixed)

This was dropped in favor of a 'state' operation, which landed in
v0.4.0 [1,2].

Although I'd prefer we'd have used --state and gotten out of the
state-registration business entirely [3,4,5].

[1]: opencontainers/runtime-spec#225
[2]: https://github.com/opencontainers/specs/releases/tag/v0.4.0
[3]: https://groups.google.com/a/opencontainers.org/d/msg/dev/q6TYqVZOcX8/W1RVyCXCCQAJ
     Subject: Re: removal of /run/opencontainer/containers, add --state?
     Date: Tue, 8 Dec 2015 15:49:57 -0800
     Message-ID: <20151208234957.GK2767@odin.tremily.us>
[4]: wking/oci-command-line-api#14
[5]: opencontainers/runtime-spec#225 (comment)