The build of my first tentative 3.9~rc1 ISO failed with:

 E: Unable to locate package ^geoclue*
 E: Couldn't find any package by glob '^geoclue*'
 E: Couldn't find any package by regex '^geoclue*'
 E: config/chroot_local-hooks/98-remove_unwanted_packages failed (exit non-zero). You should check for errors.

That's because the partial, tagged APT snapshot used to build this ISO don't
include any package whose name matches ^geoclue. So let's only attempt to remove
such packages if at least one of them is installed.