Ensure we remove existing tier labels if the MR is "not applicable"
Context
Some merge requests can start as code merge requests (at which point we would add the pipelinetier-1 label), and then could then become an MR for which we wouldn't apply tier labels anymore.
Goal
If an MR cannot have ~"pipeline::tier-" labels applied, AND it already has some ~"pipeline::tier-" label applied, we should remove those labels from the merge request.
Important: do not remove any ~pipeline::*
labels, as this list would include pipeline:expedite, and this is not a label we want to remove.