I had lots of deprecation warnings for twig engine being deprecated and other twig-related stuff that I wasn't using in my code. I have a pretty simple Symfony 4.2 (standardly installed with symfony flex) project and had a hard time locating the source of the problem.

Turns out that in the framework.yaml file (config/packages dir), from Symfony 4.2 there's still this part:

    templating:
        engines:
            - 'twig'

Removing that solved lots of deprecation issues.

Would be great if this can be added to the UPGRADE-4.3.md document