DSC fixup

Replace all objects by new ones from the current libraries
shipped by Kicad.

This causes a slightly different OSHW (Opensource Hardware)
logo to be used in the PCB.

To maintain schematic parity, all mechanical objects on the
PCB (mounting holes and OSHW logo) have their schematic
counterparts now.

dsoxlan.kicad_prl

@@ -1,7 +1,7 @@
 {
   "board": {
     "active_layer": 0,
-    "active_layer_preset": "All Layers",
+    "active_layer_preset": "",
     "auto_track_width": true,
     "hidden_netclasses": [],
     "hidden_nets": [],