Deprecate buggy attributes in Repositories API

The Repositories API contributors endpoint has returned additions and
deletions values of zero since 2014. Due to the complexity of fixing
the logic to pull the data, this instead announces the deprecation of
these attributes.

changelogs/unreleased/235797-fix-issues-analytics-feature-name.yml

+---
+title: Deprecate additions and deletions attributes in Repositories API
+merge_request: 39653
+author:
+type: deprecated

doc/api/repositories.md

@@ -199,6 +199,9 @@ authentication if the repository is publicly accessible.
 GET /projects/:id/repository/contributors
 ```
 
+CAUTION: **Deprecation:**
+The `additions` and `deletions` attributes are deprecated [as of GitLab 13.4](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39653) because they [always return `0`](https://gitlab.com/gitlab-org/gitlab/-/issues/233119).
+
 Parameters:
 
 - `id` (required) - The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user
@@ -212,14 +215,14 @@ Response:
   "name": "Example User",
   "email": "example@example.com",
   "commits": 117,
-  "additions": 2097,
-  "deletions": 517
+  "additions": 0,
+  "deletions": 0
 }, {
   "name": "Sample User",
   "email": "sample@example.com",
   "commits": 33,
-  "additions": 338,
-  "deletions": 244
+  "additions": 0,
+  "deletions": 0
 }]
 ```