pgsql: Remove the refint extension.

Remove the refint extension.

refint was sample code from the pre-built-in-FK era and has long
been documented as superseded by the built-in foreign key
mechanism. Recent fixes (see commits b0b6196386, 8cfbdf8f4d,
260e97733b, 611756948e, 1fbe2066dc, and 1541d91d1c) made it clear
that the code has more issues than its sample-code value justifies.

Author: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reviewed-by: solai v <solai(dot)cdac(at)gmail(dot)com>
Reviewed-by: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAJTYsWUHq8Ohc6-N-xamOPYz-q3qUYMtwQX-1%3DZi%3D5N1Q_GSEQ%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5e90e0914cfa9345de35efd34eb7a94b59bc23b5

Modified Files
--------------
contrib/spi/Makefile | 13 +-
contrib/spi/expected/refint.out | 113 ------
contrib/spi/meson.build | 30 --
contrib/spi/refint--1.0.sql | 14 -
contrib/spi/refint.c | 538 -------------------------
contrib/spi/refint.control | 5 -
contrib/spi/refint.example | 82 ----
contrib/spi/sql/refint.sql | 97 -----
doc/src/sgml/appendix-obsolete-refint.sgml | 24 ++
doc/src/sgml/appendix-obsolete.sgml | 1 +
doc/src/sgml/contrib-spi.sgml | 107 -----
doc/src/sgml/filelist.sgml | 1 +
src/test/perl/PostgreSQL/Test/AdjustUpgrade.pm | 15 +
13 files changed, 45 insertions(+), 995 deletions(-)