The flutter engine has moved from github.com/flutter/engine to github.com/flutter/flutter in the engine directory. There are places where documentation and code comments have not migrated.

Github search to find references.
https://github.com/search?q=repo%3Aflutter%2Fflutter+https%3A%2F%2Fgithub.com%2Fflutter%2Fengine&type=code&p=2

Leave any references for specific pull requests or commit hashes.