chore: Use RAII for erasing the WireGuard device in rp

This, for now, disables correct handling of program termination,
but not because the RAII does not work. Instead, we need to implement
a proper signal handling concept.

We also removed some teardown handlers which are not covered by RAII,
like removing the routes we set up. The reason for this is, that this
is going to be taken care of by removing the wireguard device anyway.

rp/Cargo.toml

@@ -25,7 +25,7 @@ rosenpass = { workspace = true }
 rosenpass-ciphers = { workspace = true }
 rosenpass-cipher-traits = { workspace = true }
 rosenpass-secret-memory = { workspace = true }
-rosenpass-util = { workspace = true }
+rosenpass-util = { workspace = true, features = ["tokio"] }
 rosenpass-wireguard-broker = { workspace = true }
 
 tokio = { workspace = true }