Remove echo command from validation steps.

Echo command does not exist in windows and fails on windows builders.

Change-Id: I8ff4ce7b721e8b5955414f2ba6e62353d3300a5c
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/6380
Commit-Queue: Godofredo Contreras <godofredoc@google.com>
Reviewed-by: Chris Yang <ychris@google.com>