Move the CHANGELOG entry for dart:cli deprecation to 2.15.0
Move the CHANGELOG entry for dart:cli deprecation to 2.15.0

Change-Id: I73bfdd310af6df6cc1d62311e155fc432b84165d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212567
Commit-Queue: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Auto-Submit: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@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