Migrator: Only print text about --apply-changes conditionally
Migrator: Only print text about --apply-changes conditionally

Fixes https://github.com/dart-lang/sdk/issues/40881

Change-Id: I4671e29f05ca9495419681a1f3fcb9d1718acbf8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147334
Reviewed-by: Mike Fairhurst <2002604e76601be549134505841fea93de80dc45@google.com>
Reviewed-by: Paul Berry <72d414e3a99fb120308437779d51667bcc0984eb@google.com>
Commit-Queue: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk