To allow transition to FilterLabel without breaking existing, Filter-based code,
DM-27169 introduced getFilterLabel() methods on Exposure and ExposureFitsReader as well as a .filterLabel component in the Butler. However, the preferred API uses getFilter() and .filter, which is freed up in DM-27177.
Per current deprecation rules, all in-Stack migration back to filter as the API name should have been done on
DM-27177; once nobody is using FilterLabel except as a class name, remove the transitional APIs.