Remove IDs deprecated in v1.3 from 1.5

[kolyshkin]

There are a few things that were deprecated in v1.3 or earlier:

• the entirety of libcontainer/configs/cgroup_deprecated.go
• RunHooks in libcontainer/configs/config.go
• libcontainer/user package
• libcontainer/userns package

This should be removed before 1.5-rc1.

Ideally, we should also deprecate the rest of libcontainer/devices as we're not using it ourselves, but it's hard to say what to recommend instead (maybe we need to move it to under moby/sys as suggested in moby/sys#181).