The tag is present in Lintian version 2.108.13. That is the most recent version we know about.
The maintainer script doesn't seem to contain any code other than comments and boilerplate (set -e, exit statements, and the case statement to parse options). While this is harmless in most cases, it is probably not what you wanted, may mean the package will leave unnecessary files behind until purged, and may even lead to problems in rare situations where dpkg would fail if no maintainer script was present.
If the package currently doesn't need to do anything in this maintainer script, it shouldn't be included in the package.