get rid of dead asset zcl

[buck54321]

Also switches to using importall package in bisonw-desktop.

Does not delete the client/asset/zcl or server/asset/zcl or testing packages yet. We can do that any time, but it might be worth discussing a way to handle low-cap assets that enables them to be switched on by the user somehow, so I'll leave the code for now.

I highly doubt anybody is using bw as a Zclassic wallet, but it doesn't matter if they are, since the only option for wallet type is the external RPC wallet.