GCC: fix some unused warnings

hash_extra: don't test for success in `jh_hash` and `skein_hash` since its guaranteed
device_ledger: move anonymous global variable apdu_verbose into .cpp file
Add comments to `refreshed` method variable in wallet2

src/device/device_ledger.cpp

@@ -43,6 +43,10 @@ namespace hw {
 
   #ifdef WITH_DEVICE_LEDGER
 
+    namespace {
+        bool apdu_verbose =true;
+    }
+
     #undef MONERO_DEFAULT_LOG_CATEGORY
     #define MONERO_DEFAULT_LOG_CATEGORY "device.ledger"