pgsql: Revert "Allow on-line enabling and disabling of data checksums"

Revert "Allow on-line enabling and disabling of data checksums"

This reverts the backend sides of commit 1fde38beaa0c3e66c340efc7cc0dc272d6254bb0.
I have, at least for now, left the pg_verify_checksums tool in place, as
this tool can be very valuable without the rest of the patch as well,
and since it's a read-only tool that only runs when the cluster is down
it should be a lot safer.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/a228cc13aeabff308d6dfc98a1015865f5393fce

Modified Files
--------------
doc/src/sgml/func.sgml                            |  65 --
doc/src/sgml/ref/initdb.sgml                      |   6 +-
doc/src/sgml/reference.sgml                       |   1 -
doc/src/sgml/wal.sgml                             |  81 --
src/backend/access/rmgrdesc/xlogdesc.c            |  16 -
src/backend/access/transam/xlog.c                 | 124 +---
src/backend/access/transam/xlogfuncs.c            |  59 --
src/backend/catalog/system_views.sql              |   5 -
src/backend/postmaster/Makefile                   |   5 +-
src/backend/postmaster/bgworker.c                 |   7 -
src/backend/postmaster/checksumhelper.c           | 855 ----------------------
src/backend/postmaster/pgstat.c                   |   5 -
src/backend/replication/basebackup.c              |   2 +-
src/backend/replication/logical/decode.c          |   1 -
src/backend/storage/ipc/ipci.c                    |   2 -
src/backend/storage/page/README                   |   3 +-
src/backend/storage/page/bufpage.c                |   6 +-
src/backend/utils/misc/guc.c                      |  37 +-
src/bin/pg_upgrade/controldata.c                  |   9 -
src/bin/pg_upgrade/pg_upgrade.h                   |   2 +-
src/bin/pg_verify_checksums/pg_verify_checksums.c |   5 +-
src/include/access/xlog.h                         |  10 +-
src/include/access/xlog_internal.h                |   7 -
src/include/catalog/pg_control.h                  |   1 -
src/include/catalog/pg_proc.dat                   |   8 -
src/include/pgstat.h                              |   4 +-
src/include/postmaster/checksumhelper.h           |  31 -
src/include/storage/bufpage.h                     |   1 -
src/include/storage/checksum.h                    |   7 -
src/test/Makefile                                 |   3 +-
src/test/checksum/.gitignore                      |   2 -
src/test/checksum/Makefile                        |  24 -
src/test/checksum/README                          |  22 -
src/test/checksum/t/001_standby_checksum.pl       | 101 ---
src/test/isolation/expected/checksum_cancel.out   |  27 -
src/test/isolation/expected/checksum_enable.out   |  27 -
src/test/isolation/isolation_schedule             |   4 -
src/test/isolation/specs/checksum_cancel.spec     |  47 --
src/test/isolation/specs/checksum_enable.spec     |  70 --
39 files changed, 34 insertions(+), 1658 deletions(-)