un-deperate contracthash during testing

Avoids a rust test runner bug, see https://github.com/rust-lang/rust/issues/47238

src/util/contracthash.rs

@@ -18,7 +18,7 @@
 //! at http://blockstream.com/sidechains.pdf for details of
 //! what this does.
 
-#![deprecated]
+#![cfg_attr(not(test), deprecated)]
 
 use secp256k1::{self, Secp256k1};
 use PrivateKey;