pgsql: Remove XLOG_HEAP2_VISIBLE entirely

Remove XLOG_HEAP2_VISIBLE entirely

There are no remaining users that emit XLOG_HEAP2_VISIBLE records, so it
can be removed. This includes deleting the xl_heap_visible struct and
all functions responsible for emitting or replaying XLOG_HEAP2_VISIBLE
records.

Bumps XLOG_PAGE_MAGIC because we removed a WAL record type.

Author: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/a881cc9c7e819fb26b73bb43b35d43db6b795cc7

Modified Files
--------------
src/backend/access/common/bufmask.c | 5 +-
src/backend/access/heap/heapam.c | 54 +----------
src/backend/access/heap/heapam_xlog.c | 156 ++-----------------------------
src/backend/access/heap/pruneheap.c | 4 +-
src/backend/access/heap/vacuumlazy.c | 16 ++--
src/backend/access/heap/visibilitymap.c | 151 ++++++------------------------
src/backend/access/rmgrdesc/heapdesc.c | 10 --
src/backend/replication/logical/decode.c | 1 -
src/backend/storage/ipc/standby.c | 9 +-
src/include/access/heapam_xlog.h | 21 +----
src/include/access/visibilitymap.h | 13 +--
src/include/access/visibilitymapdefs.h | 9 --
src/include/access/xlog_internal.h | 2 +-
src/tools/pgindent/typedefs.list | 1 -
14 files changed, 65 insertions(+), 387 deletions(-)