This PR does the following:
1. Suppresses underground buildings from rendering, when such buildings are tagged `location=underground`. Based on the wiki documentation, the `layer` tag does not determine whether a feature is above of below ground.
2. Unifies the building and building relation imposm exclusion mappings.
The following underground building feature in Luxembourg is used as the test object:
https://www.openstreetmap.org/way/582873794
5833e8ce6e