fix some recent rustc warnings

src/util/address.rs

@@ -137,7 +137,6 @@ impl Address {
     /// Create a witness pay to script hash address
     pub fn p2wsh (script: &script::Script, network: Network) -> Address {
         use bitcoin_hashes::sha256;
-        use bitcoin_hashes::Hash;
 
         Address {
             network: network,
@@ -156,8 +155,6 @@ impl Address {
     /// This is a segwit address type that looks familiar (as p2sh) to legacy clients
     pub fn p2shwsh (script: &script::Script, network: Network) -> Address {
         use bitcoin_hashes::sha256;
-        use bitcoin_hashes::Hash;
-        use bitcoin_hashes::hash160;
 
         let ws = script::Builder::new().push_int(0)
                                        .push_slice(&sha256::Hash::hash(&script[..])[..])

src/util/psbt/raw.rs

@@ -43,9 +43,12 @@ pub struct Pair {
 
 impl fmt::Display for Key {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use hex;
-
-        write!(f, "type: {:#x}, key: {}", self.type_value, hex::encode(&self.key))
+        write!(
+            f,
+            "type: {:#x}, key: {}",
+            self.type_value,
+            ::hex::encode(&self.key)
+        )
     }
 }