travel-sample has too many indexes

All the indexes (20+) that are part of travel-sample mean the indexer can be pegged to 400% cpu (aws ec2 t2.xlarge) for minutes at a time, leading to a suboptimal developer experience.

Aside, these indexes are configured with "defer build" of true, which means a user will see errors (for minutes) until the primary index is finally built.

related: https://github.com/couchbaselabs/smallcb/issues/39