The new libfprint version has support for devices that store data on the
sensor. In that case, the on-sensor storage might fill up when the user
tries to enroll a new print.

The strategy introduced here to handle this is to try and delete prints
from the device that we do not know about (assuming, it is e.g. from an
old installation and unusable).

It can also happen that we are not able to garbage collect old prints.
If that happens, a new error code "enroll-data-full" will be returned
signalling the situation to the enrolling application.