Suppress messages in composer output when there were no actual changes

[aleksblendwerk]

Right now, Flex always outputs

Synchronizing package.json with PHP packages
Don't forget to run npm install --force or yarn install --force to refresh your Javascript dependencies!
Run composer recipes at any time to see the status of your Symfony recipes.

when running composer update, even when there is Nothing to install, update or remove or no changes have effectively been made.

I think this should only be printed when any changes have actually been made.

[nicolas-grekas]

Fixed by #841 if I'm not wrong.