pgsql: Revert recovery prefetching feature.

Revert recovery prefetching feature.

This set of commits has some bugs with known fixes, but at this late
stage in the release cycle it seems best to revert and resubmit next
time, along with some new automated test coverage for this whole area.

Commits reverted:

dc88460c: Doc: Review for "Optionally prefetch referenced data in recovery."
1d257577: Optionally prefetch referenced data in recovery.
f003d9f8: Add circular WAL decoding buffer.
323cbe7c: Remove read_page callback from XLogReader.

Remove the new GUC group WAL_RECOVERY recently added by a55a9847, as the
corresponding section of config.sgml is now reverted.

Discussion: https://postgr.es/m/CAOuzzgrn7iKnFRsB4MHp3UisEQAGgZMbk_ViTN4HV4-Ksq8zCg%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c2dc19342e05e081dc13b296787baa38352681ef

Modified Files
--------------
doc/src/sgml/config.sgml                       |   83 --
doc/src/sgml/monitoring.sgml                   |   86 +-
doc/src/sgml/wal.sgml                          |   15 -
src/backend/access/transam/Makefile            |    1 -
src/backend/access/transam/generic_xlog.c      |    6 +-
src/backend/access/transam/twophase.c          |   14 +-
src/backend/access/transam/xlog.c              |  188 ++-
src/backend/access/transam/xlogprefetch.c      |  923 --------------
src/backend/access/transam/xlogreader.c        | 1545 +++++++-----------------
src/backend/access/transam/xlogutils.c         |   49 +-
src/backend/catalog/system_views.sql           |   14 -
src/backend/postmaster/pgstat.c                |  103 +-
src/backend/replication/logical/decode.c       |    2 +-
src/backend/replication/logical/logical.c      |   26 +-
src/backend/replication/logical/logicalfuncs.c |   13 +-
src/backend/replication/slotfuncs.c            |   18 +-
src/backend/replication/walsender.c            |   42 +-
src/backend/storage/freespace/freespace.c      |    3 +-
src/backend/storage/ipc/ipci.c                 |    3 -
src/backend/utils/misc/guc.c                   |   53 +-
src/backend/utils/misc/postgresql.conf.sample  |    6 -
src/bin/pg_rewind/parsexlog.c                  |  109 +-
src/bin/pg_waldump/pg_waldump.c                |  160 ++-
src/include/access/xlog.h                      |    1 -
src/include/access/xlogprefetch.h              |   82 --
src/include/access/xlogreader.h                |  278 ++---
src/include/access/xlogutils.h                 |    7 +-
src/include/catalog/catversion.h               |    2 +-
src/include/catalog/pg_proc.dat                |    8 -
src/include/pgstat.h                           |   26 -
src/include/replication/logical.h              |    9 +-
src/include/utils/guc.h                        |    4 -
src/include/utils/guc_tables.h                 |    1 -
src/test/regress/expected/rules.out            |   11 -
src/tools/pgindent/typedefs.list               |    4 -
35 files changed, 815 insertions(+), 3080 deletions(-)