pgsql: Revert "Use CP_SMALL_TLIST for hash aggregate"

Revert "Use CP_SMALL_TLIST for hash aggregate"

This reverts commit 4cad2534da6d17067d98cf04be2dfc1bda8f2cd0 due to a
performance regression. It will be replaced by a new approach in an
upcoming commit.

Reported-by: Andres Freund
Discussion: https://postgr.es/m/20200614181418.mx4bvljmfkkhoqzl@alap3.anarazel.de
Backpatch-through: 13

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0babd109801e5ecd90df29589c23c6daf3ae69f7

Modified Files
--------------
contrib/postgres_fdw/expected/postgres_fdw.out |  4 ++--
src/backend/optimizer/plan/createplan.c        | 28 ++++----------------------
2 files changed, 6 insertions(+), 26 deletions(-)