[EventDispatcher] simplified code for TraceableEventDispatcher
feature #10200 [EventDispatcher] simplified code for TraceableEventDispatcher (fabpot)

This PR was merged into the 2.5-dev branch.

Discussion
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[EventDispatcher] simplified code for TraceableEventDispatcher

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

Commits
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42e4c7b [EventDispatcher] simplified code for TraceableEventDispatcher