WIP: Add support for new libfprint delete_finger API

This is the corresponding change for the changes in libfprint!54 (closed).

I believe that this constitutes a small change to the DBus API as the device now needs to be opened when deleting a print (it already needed to be present).

Note that proper versioning/dependencies are not yet in place in either patch.

Thanks to @vincenth for writing this. I just split it into smaller chunks and cleaned up the whitespace slighty.