Revert "Only use admin_levels from ways."

This reverts commit b0842bd7a34d761618d405200778909a09ee1655.

Refs #348 #344

https://github.com/gravitystorm/openstreetmap-carto/pull/348#issuecomment-35800733

If this is making some boundaries disappear, then this clearly
needs a different approach or much more discussion.