eipp: make no difference between remove & purge

eipp: make no difference between remove & purge

For the order there is no inherent difference between delete or purge,
so we don't tell the planer about this and instead decide in apt if a
package should be purged or not which also allows us to not tell the
planer about rc-only purges as we can trivially do this on our on as
there is no need to plan such purges.