htlcswitch: fix duplicate close

The decayed log database opening and closing is managed at a higher
level in config_builder.go.

go.mod

@@ -46,7 +46,7 @@ require (
 	github.com/lightningnetwork/lnd/cert v1.1.0
 	github.com/lightningnetwork/lnd/clock v1.1.0
 	github.com/lightningnetwork/lnd/healthcheck v1.2.0
-	github.com/lightningnetwork/lnd/kvdb v1.2.4
+	github.com/lightningnetwork/lnd/kvdb v1.2.5
 	github.com/lightningnetwork/lnd/queue v1.1.0
 	github.com/lightningnetwork/lnd/ticker v1.1.0
 	github.com/ltcsuite/ltcd v0.0.0-20190101042124-f37f8bf35796