pgsql: Remove secondary checkpoint

Remove secondary checkpoint

Previously server reserved WAL for last two checkpoints,
which used too much disk space for small servers.

Bumps PG_CONTROL_VERSION

Author: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Reviewed-by: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4b0d28de06b28e57c540fca458e4853854fbeaf8

Modified Files
--------------
doc/src/sgml/backup.sgml | 2 +-
doc/src/sgml/func.sgml | 5 --
src/backend/access/transam/xlog.c | 93 ++++++++-------------------------
src/backend/utils/misc/pg_controldata.c | 79 +++++++++++++---------------
src/bin/pg_controldata/pg_controldata.c | 3 --
src/bin/pg_resetwal/pg_resetwal.c | 1 -
src/include/catalog/pg_control.h | 3 +-
src/include/catalog/pg_proc.h | 2 +-
8 files changed, 62 insertions(+), 126 deletions(-)