Remove NotValidXyzResultImpl classes.
Remove NotValidXyzResultImpl classes.

After the breaking change we don't produce these results anymore.

Change-Id: I365b5215fef0ac857e157cc776f7fc75ea20702c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/206481
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@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