[EventDispathcer] Fix removeListener

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Todo

- [x] Add a UT

I won't have time to add a test before next Friday but this PR could save some debugging (especially with Silex & Closures)