CHANGELOG: Move entry for HTTP header redirect changes to 2.16.0
CHANGELOG: Move entry for HTTP header redirect changes to 2.16.0

Related to commits

- master branch 57db739be0ad4629079bfa94840064f615d35abc
- stable (2.16.0) branch f5bb0b33f5c5d08099e48a26bf37b407428a52a2

Change-Id: Iad8d84600c870e4b819fc6c62fbb4d6861a575de
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/231161
Reviewed-by: Brian Quinlan <2ba0baab12cbdc73959f1aa8397b55b4d7de9371@google.com>
Auto-Submit: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@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