graph/db+sqldb: improve performance of chan update sql migration

This commit simplifies insertChanEdgePolicyMig. Much of the logic can be
removed given that this method is only used in the context of the graph
SQL migration.

This should improve the performance of the migration quite a lot since
it removes the extra GetChannelAndNodesBySCID call.

graph/db/sql_store.go

@@ -124,7 +124,7 @@ type SQLQueries interface {
 	GetChannelPolicyByChannelAndNode(ctx context.Context, arg sqlc.GetChannelPolicyByChannelAndNodeParams) (sqlc.GraphChannelPolicy, error)
 	GetV1DisabledSCIDs(ctx context.Context) ([][]byte, error)
 
-	InsertChanPolicyExtraType(ctx context.Context, arg sqlc.InsertChanPolicyExtraTypeParams) error
+	UpsertChanPolicyExtraType(ctx context.Context, arg sqlc.UpsertChanPolicyExtraTypeParams) error
 	GetChannelPolicyExtraTypesBatch(ctx context.Context, policyIds []int64) ([]sqlc.GetChannelPolicyExtraTypesBatchRow, error)
 	DeleteChannelPolicyExtraTypes(ctx context.Context, channelPolicyID int64) error
 
@@ -3934,8 +3934,8 @@ func upsertChanPolicyExtraSignedFields(ctx context.Context, db SQLQueries,
 
 	// Insert all new extra signed fields for the channel policy.
 	for tlvType, value := range extraFields {
-		err = db.InsertChanPolicyExtraType(
-			ctx, sqlc.InsertChanPolicyExtraTypeParams{
+		err = db.UpsertChanPolicyExtraType(
+			ctx, sqlc.UpsertChanPolicyExtraTypeParams{
 				ChannelPolicyID: chanPolicyID,
 				Type:            int64(tlvType),
 				Value:           value,