Introduce composer-unused check

[mmenozzi]

No description provided.

[lchrusciel]

Hey @mmenozzi - can we exclude flex from the check?

[mmenozzi]

Hi @lchrusciel, sorry for my late reply...
symfony/flex is already ignored (see here) indeed the build is not failing. But it appears that the github output mode puts a warning annotation on the symfony/flex package anyway.

This is the raw output using the default mode and the github mode:

If you prefer I can switch to the default output but we'll loose error annotations in the CI summary, like this:

Maybe it's better to loose errors in CI summary instead of having a warning for symfony/flex for every build...

Or maybe we can do this "hack" to exclude warnings from the github output:

php composer-unused.phar -o github | grep -v "::warning"

Let me know.