Remove 'Leave Project' and 'Leave Group' from settings dropdowns

## What does this MR do?

Removes `Leave Project` and `Leave Group` from the settings dropdown.

Adds it to the `views/shared/members/access_request_buttons.html.haml`.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

![Screen_Shot_2016-11-19_at_15.34.26](/uploads/5c66a025513b4780a9e881f0036381e4/Screen_Shot_2016-11-19_at_15.34.26.png)
![Screen_Shot_2016-11-19_at_15.35.29](/uploads/ed74a5dfe982cf65bb49c0c4fb307061/Screen_Shot_2016-11-19_at_15.35.29.png)

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #23305

See merge request !7600