mod+kvdb+channeldb: use btcwallet new DB interface

Depends on btcsuite/btcwallet#757.
Pulls in the updated version of btcwallet and walletdb that have the DB
interface enhanced by their own View() and Update() methods with the
reset callback/closure supported out of the box. That way the global
package-level View() and Update() functions now become pure redirects.

chainntnfs/test/test_interface.go

@@ -1926,7 +1926,9 @@ func TestInterfaces(t *testing.T, targetBackEnd string) {
 		testCfg := chainntnfs.CacheConfig{
 			QueryDisable: false,
 		}
-		hintCache, err := chainntnfs.NewHeightHintCache(testCfg, db)
+		hintCache, err := chainntnfs.NewHeightHintCache(
+			testCfg, db.Backend,
+		)
 		if err != nil {
 			t.Fatalf("unable to create height hint cache: %v", err)
 		}