pgsql: Revert function to get memory context stats for processes

Revert function to get memory context stats for processes

Due to concerns raised about the approach, and memory leaks found
in sensitive contexts the functionality is reverted. This reverts
commits 45e7e8ca9, f8c115a6c, d2a1ed172, 55ef7abf8 and 042a66291
for v18 with an intent to revisit this patch for v19.

Discussion: https://postgr.es/m/594293.1747708165@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fb844b9f06568aa29303122ac0bb7b4c3cce2542

Modified Files
--------------
doc/src/sgml/func.sgml                          | 171 -------
doc/src/sgml/release-18.sgml                    |  15 -
src/backend/catalog/system_views.sql            |   5 -
src/backend/postmaster/autovacuum.c             |   4 -
src/backend/postmaster/checkpointer.c           |   4 -
src/backend/postmaster/interrupt.c              |   4 -
src/backend/postmaster/pgarch.c                 |   4 -
src/backend/postmaster/startup.c                |   4 -
src/backend/postmaster/walsummarizer.c          |   4 -
src/backend/storage/ipc/ipci.c                  |   3 -
src/backend/storage/ipc/procsignal.c            |   3 -
src/backend/storage/lmgr/lwlock.c               |   2 -
src/backend/storage/lmgr/proc.c                 |   1 -
src/backend/tcop/postgres.c                     |   3 -
src/backend/utils/activity/wait_event_names.txt |   1 -
src/backend/utils/adt/mcxtfuncs.c               | 426 ++--------------
src/backend/utils/adt/pg_locale.c               |   1 +
src/backend/utils/init/globals.c                |   1 -
src/backend/utils/init/postinit.c               |   7 -
src/backend/utils/mb/mbutils.c                  |   1 +
src/backend/utils/mmgr/mcxt.c                   | 646 +-----------------------
src/include/catalog/pg_proc.dat                 |  10 -
src/include/miscadmin.h                         |   1 -
src/include/storage/lwlock.h                    |   2 -
src/include/storage/procsignal.h                |   1 -
src/include/utils/memutils.h                    |  82 ---
src/test/regress/expected/sysviews.out          |  19 -
src/test/regress/sql/sysviews.sql               |  18 -
src/tools/pgindent/typedefs.list                |   4 -
29 files changed, 47 insertions(+), 1400 deletions(-)