chainntnfs: move cache implementation to channeldb

This commit moves the `HeightHintCache` implementation to the
`channeldb` package and inverts the dependency relation between
`chainntnfs` and `channeldb`.

Many packages depend on channeldb for type definitions,
interfaces, etc. `chainntnfs` is an example of that. `chainntnfs`
defines the  `SpendHintCache` and `ConfirmHintCache` interfaces but
it also implments them (`HeightHintCache` struct). The implementation
uses logic that should not leak from channeldb (ex: bucket paths).
This makes our code highly coupled + it would not allow us to use any
of these interfaces in a package that is imported by `channeldb`
(circular dependency).

chainntnfs/btcdnotify/btcd_test.go

@@ -29,7 +29,7 @@ var (
 	}
 )
 
-func initHintCache(t *testing.T) *chainntnfs.HeightHintCache {
+func initHintCache(t *testing.T) *channeldb.HeightHintCache {
 	t.Helper()
 
 	db, err := channeldb.Open(t.TempDir())
@@ -38,10 +38,10 @@ func initHintCache(t *testing.T) *chainntnfs.HeightHintCache {
 		require.NoError(t, db.Close())
 	})
 
-	testCfg := chainntnfs.CacheConfig{
+	testCfg := channeldb.CacheConfig{
 		QueryDisable: false,
 	}
-	hintCache, err := chainntnfs.NewHeightHintCache(testCfg, db.Backend)
+	hintCache, err := channeldb.NewHeightHintCache(testCfg, db.Backend)
 	require.NoError(t, err, "unable to create hint cache")
 
 	return hintCache