Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Use case

We rolled back ICU in Chromium, and flutter engine should follow. For some reason, the auto-rolled does not allow for rollbacks, so this needs to happen manually.

A generated manual roll at:
flutter/engine#42794 failed for some merge conflict that I couldn't discern.

Proposal

I will make a PR to roll the ICU in flutter/engine/DEPS to the appropriate commit ID.