Fix naming of the heavy crossbow ("Ganz-Rustung").

The only source for the name "Ganz-Rustung" are a few posts in
<http://thearbalistguild.forumotion.com/t22p30-medieval-crossbows-photos-drawings-diagrams>.
I talked to the contributor (?) of the heavy crossbow and this thread was
their source. As a German with some exposure to the middle age reenactor
scene, I have never ever heard of a crossbow referred to as "Rüstung",
it is in this context purely a term for armor. Most likely the source of
the name visited a museum and confused the labels on two showcases.