The only API user currently seems to be the examples. fprintd has its
own storage and that will be a good idea in general.
So deprecate the API, we'll need to find a different solution for the
examples eventually.
Use GPtrArray to simplify the implementation.
libfprint/fpi-data.c:777:13: warning: Access to field 'data' results in a dereference of a null pointer (loaded from variable 'elem')
list[i] = elem->data;
^~~~~~~~~~
libfprint/fpi-data.c:497:7: warning: 2nd function call argument is an uninitialized value
if (!fp_dev_supports_print_data(dev, fdata)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~