Keep deprecation of valid_actions until Chef 13.

This replaces https://github.com/opscode/chef/pull/1662.

@btm I've looked at your notes and made the necessary changes. I don't think we need to do this tough:

```
Add a deprecation warning in lib/chef/resource/lwrp_base.rb after if defined?(@actions)
```

I believe the line after `if defined?(@actions)` makes sure that the bc-compatible logic works. We already have a depr message in place. That line needs to be removed in Chef 13 IMO.