pgsql: Further post-revert cleanup after online checksums

Further post-revert cleanup after online checksums

When reverting I had missed updating the documentation for tracking data
checksum failures and the checksum version in the REDO record. The test-
code for enabling and disabling checksums offline was originally kept to
minimize backpatching conflicts, but the amount of testcode backpatching
doesn't really warrant keeping dead code.

Since no version has been shipped since bumping XLOG_PAGE_MAGIC it is
left at the previous bump version.

Reported-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reported-by: Manuel Reyes Bravo <manuelreyesbravo(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHGQGwFLNCA9nVHSsC_=G_mvsK_fAFb+QbJAL7=R9cK2PL9ZBQ@mail.gmail.com

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6b0760a10a32f2471c22eed7102f77c18d836423

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 15 +++++--------
src/include/access/xlog_internal.h | 1 -
src/test/perl/PostgreSQL/Test/Cluster.pm | 36 --------------------------------
3 files changed, 5 insertions(+), 47 deletions(-)