minor symfony#31994 [HttpKernel] Remove TestEventDispatcher (derrabus)

This PR was merged into the 3.4 branch.

Discussion
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[HttpKernel] Remove TestEventDispatcher

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

This class seems to be an orphaned test fixture. Let's delete it.

Commits
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48be09f [HttpKernel] Remove TestEventDispatcher.

Author: fabpot