Remove print_debug flag from cosmwasm-vm

[webmaster128]

With the new set_debug_handler coming in CosmWasm 1.4, there is no need to have a default implementation of the debug handler anymore. This code

            if print_debug {
                e.set_debug_handler(Some(Rc::new(RefCell::new(
                    |msg: &str, _gas_remaining: DebugInfo<'_>| {
                        eprintln!("{msg}");
                    },
                ))))
            }

can move into libwasmvm. Then cosmwasm-vm by default has no debug implementation and callers (libwasmvm, integration tests, cw-sdk, ...) can just do something like

    deps.set_debug_handler(move |msg, _info| {
        eprintln!("{msg}");
    });

if this is what they want to do. This might create a bit of work here and there, but dumping to STDERR from low level code is certainly not better.

[webmaster128]

In CosmWasm/wasmvm#453, libwasmvm sets the debug handler it wants on its own. So we can remove the default implementation and leave it up to the caller to set one. By default, None is used.