Remove confusing legacy permissions from Panels Node

Panels Node creates a series of custom permissions for create, edit and delete of the "Panel" content type, in addition to the default permissions created by the Node module.

This is confusing because we end up with two permissions for the same thing, like "Edit any panel node" and "Panel: Edit any content", where they act subtly different: the Node permission can allow or deny access (by not having the permission), but the custom Panels Node permissions can only allow access (whereas removing the permission doesn't deny access).

These permissions are basically left over from Drupal 6, but are no longer necessary now that the Node module creates default permissions for all content types. I propose removing them and migrating to the new permissions!