pgsql: Remove the query_id_squash_values GUC

Remove the query_id_squash_values GUC

Commit 62d712ecfd94 introduced the capability to calculate the same
queryId for queries with different lengths of constants in a list for an
IN clause. This behavior was originally enabled with a GUC
query_id_squash_values. After a discussion about the value of such a
GUC, it was decided to back out of the use of a GUC and make the
squashing behavior the only available option.

Author: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: https://postgr.es/m/Z-LZyygkkNyA8-kR@msg.df7cb.de
Discussion: https://postgr.es/m/CA+q6zcVTK-3C-8NWV1oY2NZrvtnMCDqnyYYyk1T7WMUG65MeOQ@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/9fbd53dea5d513a78ca04834101ca1aa73b63e59

Modified Files
--------------
contrib/pg_stat_statements/expected/dml.out | 2 +-
contrib/pg_stat_statements/expected/squashing.out | 33 -----------------------
contrib/pg_stat_statements/sql/squashing.sql | 10 -------
doc/src/sgml/config.sgml | 30 ---------------------
doc/src/sgml/pgstatstatements.sgml | 6 ++---
src/backend/nodes/queryjumblefuncs.c | 16 ++++-------
src/backend/postmaster/launch_backend.c | 3 ---
src/backend/utils/misc/guc_tables.c | 10 -------
src/backend/utils/misc/postgresql.conf.sample | 1 -
src/include/nodes/queryjumble.h | 1 -
10 files changed, 8 insertions(+), 104 deletions(-)