make: remove png render

the PNG board render used pcbdraw, but this is an unstable:

- takes some time to get up to date with kicad releases
- does not support all features (such as rectangle edges)
- does not work for me since months (even git version)

thus, I decided to remove this rendering.
KiCad 9 should come with a CLI for the 3D render.
we will try with that once released.

Makefile

@@ -37,7 +37,7 @@ all: $(VERSIONED_SHEET) ${NAME}.sch.pdf ${NAME}.bom.csv render fab
 
 fab: ${FABRICATION_DIR} ${IBOM}
 
-render: ${NAME}.brd-top.png ${NAME}.brd-bot.png ${NAME}.brd-top.svg ${NAME}.brd-bot.svg ${NAME}.3d.step
+render: ${NAME}.brd-top.svg ${NAME}.brd-bot.svg ${NAME}.3d.step
 
 # generate fabrication files (gerbers/drill/BoM/PnP)
 ${FABRICATION_DIR}: ${NAME}.versioned.kicad_sch ${NAME}.versioned.kicad_pcb
@@ -62,14 +62,6 @@ lib:
 %.sch.pdf: %.versioned.kicad_sch %.versioned.kicad_pro
 	$(KICAD) sch export pdf --output $@ $<
 
-# generate render from layout (top side)
-%.brd-top.png: %.versioned.kicad_pcb
-	pcbdraw plot --silent --no-components --dpi 600 --side front $< $@
-
-# generate render from layout (bottom side)
-%.brd-bot.png: %.versioned.kicad_pcb
-	pcbdraw plot --silent --no-components --dpi 600 --side back $< $@
-
 # generate render from layout (top side)
 %.brd-top.svg: %.versioned.kicad_pcb
 	$(KICAD) pcb export svg --layers F.Cu,F.Paste,F.Silkscreen,Edge.Cuts --page-size-mode 2 --exclude-drawing-sheet --output $@ $<