ctr: use transfer service by default

Prior to this commit, `--local=false` had to be explicitly specified to
opt-in to the transfer service

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

cmd/ctr/commands/images/export.go

@@ -61,7 +61,7 @@ When '--all-platforms' is given all images in a manifest list must be available.
 			Name:  "all-platforms",
 			Usage: "Exports content from all platforms",
 		},
-		cli.BoolTFlag{
+		cli.BoolFlag{
 			Name:  "local",
 			Usage: "Run export locally rather than through transfer API",
 		},
@@ -93,7 +93,7 @@ When '--all-platforms' is given all images in a manifest list must be available.
 		}
 		defer w.Close()
 
-		if !context.BoolT("local") {
+		if !context.Bool("local") {
 			pf, done := ProgressHandler(ctx, os.Stdout)
 			defer done()