pgsql: Retire pg_standby.

Retire pg_standby.

pg_standby was useful more than a decade ago, but now it is obsolete.
It has been proposed that we retire it many times. Now seems like a
good time to finally do it, because "waiting restore commands"
are incompatible with a proposed recovery prefetching feature.

Discussion: https://postgr.es/m/20201029024412.GP5380%40telsasoft.com
Author: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/514b411a2b5226167add9ab139d3a96dbe98035d

Modified Files
--------------
contrib/Makefile | 1 -
contrib/pg_standby/.gitignore | 1 -
contrib/pg_standby/Makefile | 20 -
contrib/pg_standby/pg_standby.c | 907 ---------------------------------
doc/src/sgml/contrib.sgml | 7 +-
doc/src/sgml/filelist.sgml | 1 -
doc/src/sgml/high-availability.sgml | 17 +-
doc/src/sgml/pgstandby.sgml | 394 --------------
doc/src/sgml/ref/pgarchivecleanup.sgml | 7 -
src/backend/access/transam/xlog.c | 2 +-
src/tools/msvc/Mkvcbuild.pm | 4 +-
11 files changed, 9 insertions(+), 1352 deletions(-)