minor symfony#38363 Remove CHANGELOG files for 4.x (ro0NL)

This PR was merged into the 5.1 branch.

Discussion
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Remove CHANGELOG files for 4.x

| Q             | A
| ------------- | ---
| Branch?       | 5.0 (maintenance only)
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

See symfony#36436

Commits
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e0f90b4 Remove CHANGELOG files for 4.x

Author: fabpot