googlecloudstorage: use the s3 pacer to speed up transactions

This commit switches Google Cloud Storage from the drive pacer to the
s3 pacer. The main difference between them is that the s3 pacer does
not limit transactions in the non-error case. This is appropriate for
a cloud storage backend where you pay for each transaction.

backend/googlecloudstorage/googlecloudstorage.go

@@ -482,7 +482,7 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		name:  name,
 		root:  root,
 		opt:   *opt,
-		pacer: fs.NewPacer(ctx, pacer.NewGoogleDrive(pacer.MinSleep(minSleep))),
+		pacer: fs.NewPacer(ctx, pacer.NewS3(pacer.MinSleep(minSleep))),
 		cache: bucket.NewCache(),
 	}
 	f.setRoot(root)