pgpool: Retire Slony mode.

Retire Slony mode.

Previously Pgpool-II accepted "slony mode" as one of the
backend_clustering_mode to support Slony-I
(https://www.slony.info/) However the latest Slony-I was released in
2022, nearly 3 years ago at this point. And we heard nothing from
users about retiring Slony mode. This suggests that there would be no
active Slony-I mode users. So let's drop Slony-I support.

Author: Tatsuo Ishii <ishii(at)postgresql(dot)org>
Reviewed-by: Bo Peng <pengbo(at)sraoss(dot)co(dot)jp>
Discussion: [pgpool-general: 9486] Retiring slony mode
https://www.pgpool.net/pipermail/pgpool-general/2025-May/009489.html
Discussion: https://www.postgresql.org/message-id/20250722.153130.1007226654125839063.ishii%40postgresql.org

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=b402dbc098339aeef84e46327901139a1ee6cfa1

Modified Files
--------------
doc.ja/src/sgml/connection-settings.sgml | 23 ------------------
doc.ja/src/sgml/loadbalance.sgml | 2 +-
doc.ja/src/sgml/performance.sgml | 2 +-
doc.ja/src/sgml/restrictions.sgml | 2 +-
doc.ja/src/sgml/runtime.sgml | 26 +-------------------
doc/src/sgml/connection-settings.sgml | 29 -----------------------
doc/src/sgml/performance.sgml | 2 +-
doc/src/sgml/ref/pgpool_setup.sgml | 2 +-
doc/src/sgml/restrictions.sgml | 2 +-
doc/src/sgml/runtime.sgml | 19 +--------------
src/config/pool_config_variables.c | 1 -
src/context/pool_query_context.c | 2 +-
src/include/pool.h | 4 +---
src/include/pool_config.h | 8 -------
src/protocol/pool_proto_modules.c | 2 +-
src/sample/pgpool.conf.sample-stream | 2 +-
src/test/pgpool_setup.in | 7 +-----
src/test/regression/tests/040.client_auth/test.sh | 4 ++--
18 files changed, 15 insertions(+), 124 deletions(-)