Merge branch 'remove-duplicate-api-field' into 'master'

entities: remove :description from MergeRequest

## What does this MR do?

Removes a duplicate `description` key from API JSON objects.

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

No.

## Why was this MR needed?

`description` is already exported via `ProjectEntity` and doesn't need to be listed in `MergeRequest` as well.

## What are the relevant issue numbers?

N/A

## Screenshots (if relevant)

N/A

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5099

CHANGELOG

@@ -63,6 +63,7 @@ v 8.10.0 (unreleased)
   - Added setting to set new users by default as external !4545 (Dravere)
   - Add min value for project limit field on user's form !3622 (jastkand)
   - Add reminder to not paste private SSH keys !4399 (Ingo Blechschmidt)
+  - Remove duplicate `description` field in `MergeRequest` entities (Ben Boeckel)
 
 v 8.9.5
   - Add more debug info to import/export and memory killer. !5108

lib/api/entities.rb

@@ -199,7 +199,6 @@ module API
       expose :author, :assignee, using: Entities::UserBasic
       expose :source_project_id, :target_project_id
       expose :label_names, as: :labels
-      expose :description
       expose :work_in_progress?, as: :work_in_progress
       expose :milestone, using: Entities::Milestone
       expose :merge_when_build_succeeds