[COMMITTERS] pgsql: Use lfirst_node() and linitial_node() where appropriate inplann

Use lfirst_node() and linitial_node() where appropriate in planner.c.

There's no particular reason to target this module for the first
wholesale application of these macros; but we gotta start somewhere.

Ashutosh Bapat and Jeevan Chalke

Discussion: https://postgr.es/m/CAFjFpRcNr3r=u0ni=7A4GD9NnHQVq+dkFafzqo2rS6zy=dt1eg@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6e427aa4e5f3ad79a79b463c470daf93fa15767b

Modified Files
--------------
src/backend/optimizer/plan/planner.c | 122 +++++++++++++++++------------------
1 file changed, 61 insertions(+), 61 deletions(-)