changed all version deps to accepts all upcoming Symfony versions
removed versions in composer.json files
merged branch fabpot/dep-versions (PR #8017)

This PR was merged into the master branch.

Discussion
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changed all version deps to accept all upcoming Symfony versions

Everything is in the title.

Commits
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b1c9fd2 removed versions in composer.json files
f41ac06 changed all version deps to accepts all upcoming Symfony versions