remove parts that have DNP attribute set

[cbrake]

thinking we add an attribute named DNP set to DNP. One the schematic, this attribute would typically be set to visible.

[cbrake]

https://gitlab.com/kicad/code/kicad/-/merge_requests/901/diffs

This change did not get merged.

[cbrake]

It looks like KiCad netlist reader supports using a field:

Installed="NU"

see: https://github.com/mossmann/kicad-bom-scripts/blob/master/kicad_netlist_reader.py#L31

[cbrake]

https://forum.kicad.info/t/schematic-symbol-exclude-from-bill-of-materials/23230/7

[cbrake]

https://gitlab.com/kicad/code/kicad/-/issues/8888

[cbrake]

KiCad has an Exclude from bill of materials, but I think this is meant for parts that should not be in the BOM, like holes in board, etc, not a DNP:

[cbrake]

in /usr/share/kicad/plugins/kicad_netlist_reader.py:

# You may exclude components from the BOM by either:
#
# 1) adding a custom field named "Installed" to your components and filling it
# with a value of "NU" (Normally Uninstalled).