`Entities.streamForExport()`: don't SELECT unused columns

[alxndrsn]

The results from this query are consumed exclusively in lib/data/entity.js:

1. streamEntityCsv()
2. streamEntityCsvAttachment()
3. streamEntityOdata()

For each of these uses, confirm which of the selected columns is actually used.

Consider results with respect to:

• common unused columns
• use-specific unused columns