IBX-7782: Removed symfony/event-dispatcher-contracts direct dependency

[Steveb-p]

Question	Answer
JIRA issue	IBX-7782
Type	bug
Target Ibexa version	v4.6
BC breaks	no
Doc needed	no

It is not necessary for us to rely on symfony/event-dispatcher-contracts directly, as this dependency is declared by symfony/event-dispatcher itself.

Since we are not agnostic to event dispatcher implementation, we should not declare this dependency ourselves.

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly (main for features, the oldest supported for bugs).
• Asked for a review (ping @ibexa/engineering).