Build page shows old branch under revisions

## Issue

### Context
- **Gitlab plugin version**: 1.5.12
- **Gitlab version**: 11.10.4
- **Jenkins version**: 2.164.2
- **Job type**: Pipeline

### Logs & Traces

_Please include any relevant log that could serve to better understand the source of your issue_
For Jenkins Gitlab Plugin logs, follow instruction in [User Support section](https://github.com/jenkinsci/gitlab-plugin#user-support).
For Gitlab logs, ask an administrator to provide you the relevant Gitlab logs.

### Problem description

_Describe your problem in a meaningful way_:
Pushed to a branch in the repository. In the build page, that branch and commit were shown, as well as an old branch and commit (which is not in a pending MR and is not even present in the repository any longer). Created a new branch and the problem still exists, with the same phantom branch and commit. Attaching logs and screenshot.


[jenkins-gitlab-issue.txt](https://github.com/jenkinsci/gitlab-plugin/files/3189183/jenkins-gitlab-issue.txt)