removed listener on enter key

fixed https://github.com/sulu-cmf/sulu-standard/issues/11

- [x] finish the code
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | none
| Fixed tickets | yes
| Doc           | none