Resolves divider issue in group setting dropdown

## What does this MR do?
This MR resolves the issue #24048 
##  Are there points in the code the reviewer needs to double check?
NR
## Why was this MR needed?
This MR removes extra divider from group setting dropdown when there is only one entry to show. This improves UX
## Screenshots (if relevant)

**Before**
![dd-before](/uploads/b4696b610a921a710c6be74fbb212260/dd-before.png)

**After**
![Screen_Shot_2016-11-10_at_4.09.36_PM](/uploads/a4ff6efe92ce60837afad079398c3880/Screen_Shot_2016-11-10_at_4.09.36_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #24048

See merge request !7398