simplify index tuple descriptor initialization

When Who What
2018-09-13 06:28:42 Peter Eisentraut (petere) Closed in commitfest 2018-09 with status: Committed
2018-09-13 06:28:42 Peter Eisentraut (petere) Changed committer to petere
2018-09-12 13:18:51 Artur Zakirov (a.zakirov) New status: Ready for Committer
2018-09-12 13:18:41 Artur Zakirov (a.zakirov) Added a.zakirov as reviewer
2018-08-31 08:43:02 Peter Eisentraut (petere) Changed authors to Peter Eisentraut (petere)
2018-08-31 08:42:55 Peter Eisentraut (petere) Attached mail thread ed79a5fc-e267-b3e7-2e06-682c85f9dfaf@2ndquadrant.com
2018-08-31 08:42:55 Peter Eisentraut (petere) Created patch record