deleteUser = function(authdb, id, user, callback) {
    db.request({
        type: 'DELETE',
        url: '/' + db.encode(authdb) + '/' + db.encode(id) +
             '?rev=' + db.encode(user._rev),
        contentType: 'application/json'
    }, callback);
}
Delete user from user database.

@name deleteUser(authdb, id, user, callback)
@param {String} user database
@param {String} user id
@param {Object} user document
@param {Function} callback
@api private