modules: Mass modify relative paths for 3D Models

When moving to .pretty and the newer KiCad versions, everything is based
off of environment variables. The default environment variable
invalidates our relative paths. Rather than making the new paths
relative to the default KISYS3DMOD variable, instead, just use the
proper KISYS3DMOD variable in the install/config that will allow a
direct path from there. This will result in everything being just a bit
cleaner and should work as desired if using AB2 KiCad.