rust/smb: fix manual_unwrap_or_default

rust/smb: fix manual_unwrap_or_default

warning: match can be simplified with `.unwrap_or_default()`
   --> src/smb/smb2.rs:682:41
    |
682 |                           let _guid_vec = match state.ssn2vec_map.remove(&guid_key) {
    |  _________________________________________^
683 | |                             Some(p) => p,
684 | |                             None => {
685 | |                                 SCLogDebug!("SMBv2 response: GUID NOT FOUND");
686 | |                                 Vec::new()
687 | |                             },
688 | |                         };
    | |_________________________^ help: replace it with: `state.ssn2vec_map.remove(&guid_key).unwrap_or_default()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_unwrap_or_default
    = note: `#[warn(clippy::manual_unwrap_or_default)]` on by default