Transfer contract functions shouldn't return

[ureeves]

Summary

The functions exposed by the transfer contract shouldn't return bool since they are either pass or fail, and use a panic to signal a failure.

Possible solution design or implementation

N/A

Additional context

It's not transact per-se, but more the transfer contract. The ABI of the transfer contract returns bool for most functions, even though false is never returned. This is a holdover best addressed in a new issue. Originally posted by @ureeves in https://github.com/dusk-network/rusk/pull/830#discussion_r1149387641