mkimage: fit: erase data-size property when importing data

mkimage: fit: erase data-size property when importing data

When importing data, the data-offset property is removed and the data
content is imported inside the data property of the node.

When mkimage is run twice on the same FIT, data-size property is already
set in the second run, from the first run (via the fit_export_data
function). If we don't remove the data-size property, nothing guarantees
it matches the actual size of data within the data property. To avoid
possible mistakes when handling the data property, let's simply remove
the data-size property as well.

This also fixes an ordering issue of the data-size and data-offset
properties in FIT when comparing the FIT after one run of mkimage and a
second run. This is due to fit_export_data setting data-offset property
first (it doesn't exist so it's added) and then data-size (it doesn't
exist so it's added) for the first run, while it sets data-offset
property first (removed in fit_import_data, so it doesn't exist so it's
added) and then data-size (it exists already from the first run, so it's
simply modified) for the second run.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>