Change `remove branch` to `delete branch`

this is to match `git branch -D` from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23966
This just documents the change

doc/user/project/merge_requests/index.md

@@ -76,10 +76,10 @@ You can [search and filter the results](../../search/index.md#issues-and-merge-r
 
 ![Group Issues list view](img/group_merge_requests_list_view.png)
 
-## Removing the source branch
+## Deleting the source branch
 
-When creating a merge request, select the "Remove source branch when merge
-request accepted" option and the source branch will be removed when the merge
+When creating a merge request, select the "Delete source branch when merge
+request accepted" option and the source branch will be deleted when the merge
 request is merged.
 
 This option is also visible in an existing merge request next to the merge
@@ -87,10 +87,10 @@ request button and can be selected/deselected before merging. It's only visible
 to users with [Maintainer permissions](../../permissions.md) in the source project.
 
 If the user viewing the merge request does not have the correct permissions to
-remove the source branch and the source branch is set for removal, the merge
-request widget will show the "Removes source branch" text.
+delete the source branch and the source branch is set for deletion, the merge
+request widget will show the "Deletes source branch" text.
 
-![Remove source branch status](img/remove_source_branch_status.png)
+![Delete source branch status](img/remove_source_branch_status.png)
 
 ## Allow collaboration on merge requests across forks