Don't set random ETag header for `_all_docs` view
Don't set random ETag header for `_all_docs` view

This fixes the issue that by setting a random ETag header, we implicitly
promised that there's a chance of a cache hit where there was no chance.

For 2.0, we simply remove the random ETag without replacement, in order
to not accidentally cause useless cache bloat in clients.

COUCHDB-2859

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb