Removing unneeded downlink field from nbtree stack struct

When Who What
2019-08-14 18:33:56 Peter Geoghegan (pgeoghegan) Closed in commitfest 2019-09 with status: Committed
2019-08-14 18:33:56 Peter Geoghegan (pgeoghegan) Changed committer to pgeoghegan
2019-08-12 16:43:31 Anastasia Lubennikova (lubennikovaav) New status: Ready for Committer
2019-08-12 16:43:27 Anastasia Lubennikova (lubennikovaav) Added lubennikovaav as reviewer
2019-07-15 23:16:59 Peter Geoghegan (pgeoghegan) Changed authors to Peter Geoghegan (pgeoghegan)
2019-07-15 23:16:46 Peter Geoghegan (pgeoghegan) Attached mail thread CAH2-Wzmx+UbXt2YNOUCZ-a04VdXU=S=OHuAuD7Z8uQq-PXTYUg@mail.gmail.com
2019-07-15 23:16:46 Peter Geoghegan (pgeoghegan) Created patch record