Remove obsolete/deprecated thing

For next major version we can remove obsolete/deprecated thing. This issue should track pieces that we should take look at and remove:

* Support for --plug [switch]:[plug] notation that was used before (e.g. in fence_apc)
* Support for enable/disable instead of standard on/off (in fencing.py)

Currently, there is not enough of the code to remove :)

Start by tracing the legacy --plug [switch]:[plug] handling referenced in fence_apc and the enable/disable handling in fencing.py. Inventory the remaining obsolete paths for the next major version, then confirm that both compatibility forms have been removed without expanding beyond the pieces identified by the issue.

Written by the indexing model from the issue text.