pgsql: Revert "make immutability tests in to_json and to_jsonb complete

Revert "make immutability tests in to_json and to_jsonb complete"

This reverts commit ecd9288624a.

Expression indexes, generated columns and partition keys created with
the reverted patch in place that depend on its behavior are not
removed, but a dump and restore or a pg_upgrade will now fail to
recreate them. They need to be dropped or redefined before upgrading.

Discussion: https://postgr.es/m/179372513496.2500379.6217138376932454060@gmail.com
Discussion: https://postgr.es/m/CA+TgmoaiothgQrw9OtgsMzBUCnqJ2jdaGTbS6o3fkjCd+LfzWw@mail.gmail.com
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/4b80cba35a1507a65f3f9a7d10f76ef48225bb98

Modified Files
--------------
src/backend/utils/adt/json.c | 38 +++++++-
src/backend/utils/adt/jsonb.c | 38 +++++++-
src/backend/utils/adt/jsonfuncs.c | 105 ----------------------
src/include/utils/jsonfuncs.h | 2 -
src/test/regress/expected/sqljson.out | 165 ----------------------------------
src/test/regress/sql/sqljson.sql | 89 ------------------
6 files changed, 70 insertions(+), 367 deletions(-)