Ignore subscription cancelled warning (#7020)

* Resolve TODO #6449
* Merge refs/heads/master into fix-6449

beacon-chain/sync/subscriber.go

@@ -2,7 +2,6 @@ package sync
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"reflect"
 	"runtime/debug"
@@ -26,11 +25,6 @@ import (
 
 const pubsubMessageTimeout = 30 * time.Second
 
-var (
-	// TODO(6449): Replace this with pubsub.ErrSubscriptionCancelled.
-	errSubscriptionCancelled = errors.New("subscription cancelled by calling sub.Cancel()")
-)
-
 // subHandler represents handler for a given subscription.
 type subHandler func(context.Context, proto.Message) error
 
@@ -151,7 +145,7 @@ func (s *Service) subscribeWithBase(base proto.Message, topic string, validator
 			msg, err := sub.Next(s.ctx)
 			if err != nil {
 				// This should only happen when the context is cancelled or subscription is cancelled.
-				if err != errSubscriptionCancelled { // Only log a warning on unexpected errors.
+				if err != pubsub.ErrSubscriptionCancelled { // Only log a warning on unexpected errors.
 					log.WithError(err).Warn("Subscription next failed")
 				}
 				return