Remove second fd from couch_db_updater
Remove second fd from couch_db_updater

This reverts the change to use a second file descriptor for
couch_db_udpaters to split read and writes. This is ground work for the
next few patches that change how databases are managed.

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