multi: switch on graph SQL migration

In this commit, the graph SQL migration is added to the production
build.

config_prod.go

@@ -5,9 +5,7 @@ package lnd
 import (
 	"context"
 
-	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/kvdb"
-	"github.com/lightningnetwork/lnd/sqldb"
 	"github.com/lightningnetwork/lnd/sqldb/sqlc"
 )
 
@@ -15,15 +13,6 @@ import (
 // build tag is set.
 var RunTestSQLMigration = false
 
-// getGraphStore returns a graphdb.V1Store backed by a graphdb.KVStore
-// implementation.
-func (d *DefaultDatabaseBuilder) getGraphStore(_ *sqldb.BaseDB,
-	kvBackend kvdb.Backend,
-	opts ...graphdb.StoreOptionModifier) (graphdb.V1Store, error) {
-
-	return graphdb.NewKVStore(kvBackend, opts...)
-}
-
 // getSQLMigration returns a migration function for the given version.
 //
 // NOTE: this is a no-op for the production build since all migrations that are