xcm-builder: remove clone for clippy (#7291)

fix for:
```
error: using `clone` on type `[u8; 32]` which implements the `Copy`
trait
  --> xcm/xcm-builder/src/routing.rs:44:28
   |
44 |             message.0.push(SetTopic(unique_id.clone()));
   |                                     ^^^^^^^^^^^^^^^^^ help: try
removing the `clone` call: `unique_id`
   |
   = help: for further information visit
https://rust-lang.github.io/rust-clippy/master/index.html#clone_on_copy
   = note: `-D clippy::clone-on-copy` implied by `-D clippy::complexity`
```