[CI] Remove PHP-CS-Fixer in CI job

[Kocal]

Following #2955

Maybe in one or two weeks, before I would like to see for the next PRs if our PHP-CS-Fixer CI job and Fabbot (now as a GHA) are still out-of-sync or not.
In the past, we had to open several PRs to fixes coding style issues found by PHP-CS-Fixer, but not by Fabbot

[nicolas-grekas]

the action is running php-cs-fixer, so it won't miss anything without you knowing thanks to some failure