Updated iuse::smokebomb_act

The conversion to an empty canister is defined in the json file. The code that handles this (map::process_active_item) only looks at the reverts_to definition and erase the item if that definition is null, so the `it->make(itypes["canister_empty"])` was ignored anyway.
Adjusted the logic in `iuse::smokebomb_act` to be like `iuse::dynamite_act`.

fixes #5030