Replace deprecated tempdir dependency with tempfile (#11588)

`Tempdir` is deprecated, but the functionality has been merged into
another crate: `tempfile`. This commit removes all `tempdir` dependencies
and replaces them with `tempfile` and the equivalent bindings.

Fixes #11560

parity/db/rocksdb/mod.rs

@@ -19,7 +19,7 @@ extern crate migration_rocksdb;
 extern crate ethcore_blockchain;
 
 #[cfg(test)]
-extern crate tempdir;
+extern crate tempfile;
 
 use std::{io, fs};
 use std::sync::Arc;