pgsql: Revert changes about warnings/errors for placeholders.

Revert changes about warnings/errors for placeholders.

Revert commits 5609cc01c, 2ed8a8cc5, and 75d22069e until we have
a less broken idea of how this should work in parallel workers.
Per buildfarm.

Discussion: https://postgr.es/m/1640909.1640638123@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cab5b9ab2c066ba904f13de2681872dcda31e207

Modified Files
--------------
contrib/auth_delay/auth_delay.c | 2 +-
contrib/auto_explain/auto_explain.c | 2 +-
contrib/pg_prewarm/autoprewarm.c | 2 +-
contrib/pg_stat_statements/pg_stat_statements.c | 2 +-
contrib/pg_trgm/trgm_op.c | 2 +-
contrib/postgres_fdw/option.c | 2 +-
contrib/sepgsql/hooks.c | 2 +-
src/backend/utils/misc/guc.c | 63 +++++-----------------
src/include/utils/guc.h | 5 +-
src/pl/plperl/plperl.c | 2 +-
src/pl/plpgsql/src/pl_handler.c | 2 +-
src/pl/tcl/pltcl.c | 4 +-
src/test/modules/delay_execution/delay_execution.c | 2 +-
.../ssl_passphrase_callback/ssl_passphrase_func.c | 2 +-
src/test/modules/worker_spi/worker_spi.c | 2 +-
src/test/regress/expected/guc.out | 17 ------
src/test/regress/sql/guc.sql | 9 ----
17 files changed, 27 insertions(+), 95 deletions(-)