Remove kwiebers from BE reviewer for gitlab

Why is this change being made?

I'm not able to prioritize reviews in a timely manner or prioritize the reviews over other items. At this time it's best for me to not be a reviewer for gitlab-org/gitlab.

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what