Bunker preset requires a building tag

[tohaklim]

The military=bunker preset appears to assume building=bunker now, although I am certain this wasn't the case previously.

I also don't think building=bunker is a required tag on the wiki page, and I can think of a few scenarios (eg underground shelters) where tagging this as a building would seem incorrect or strange (eg on nodes).
This PR from 2014 also suggests building=bunker was the less desirable option.

The validation rule (which I assume is in the iD repo) also suggests adding the building tag back if removing it.

Or is the intended behaviour here to trigger rendering in some sort of scenario that requires a building=* tag?