call fn wallet_get_last_version in FFI can be reduced to only take the required parameters

[SWvheerden]

Currently the call pub unsafe extern "C" fn wallet_get_last_version(config: *mut TariCommsConfig, error_out: *mut c_int) -> *mut c_char take in the entire TariCommsConfig, this is not needed and we can reduce to only take in the required options.