We don't actually need either of the things it provides (looking up in source and built, and converting to an absolute path) so just replace it with g_build_filename() instead. This also has the advantage that it does the right thing on Windows.
This is a debug-only command line program, and we don't want plugins to have access to the animated progressbar header in the future.
This will allow us to export FuPlugin in the future without dragging in the private fu-history.h too.
Also update the structure as the documentation doesn't only describe libfwupd.
