kicad-schematic-not-part-of-project-but-in-sheets

The KiCad Project file kicad_pro contains a field sheets which is supposed to list the set of kicad_sch files referenced. However, even if some files are referenced in the sheets they still aren't part of the project.

Crysknife had a bug where we used sheets to determine if a kicad_sch was part of a project but then after returning the associated ProjectJSON wouldn't include that kicad_sch (as it wasn't actually part of the project).