Canvas/XML HUD toggle shortcut is confusing

[colingeniet]

shift-P is supposed to toggle between the custom/Canvas HUD and the FG default/XML HUD. Problems:

• The XML HUD does not actually work because it is disabled by setprop("sim/hud/visibility[1]", 0); in Nasal/displays/hud.nas
• Many users seem to hit this keybinding by accident, which disables the HUD and is quite confusing.
• This feature was (I think) designed for backward compatibility. However FG versions that do not support the canvas HUD are now very old (and significantly older than the indicated minimum supported FG version)

I am leaning towards just removing it. Any objection?

[colingeniet]

Removed in https://github.com/NikolaiVChr/flightgear-saab-ja-37-viggen/commit/25c8f1fe1690e1868da01fa69be095cdcb925265, together with the autostart shortcut.