Remove read-only server settings lc_collate and lc_ctype

The GUC settings lc_collate and lc_ctype are from a time when those
locale settings were cluster-global.  When those locale settings were
made per-database (PG 8.4), the settings were kept as read-only.  As
of PG 15, you can use ICU as the per-database locale provider, so
examining these settings is already less meaningful and possibly
confusing, since you need to look into pg_database to find out what is
really happening, and they would likely become fully obsolete in the
future anyway.

Reviewed-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://www.postgresql.org/message-id/696054d1-bc88-b6ab-129a-18b8bce6a6f0@enterprisedb.com

contrib/citext/sql/citext_utf8.sql

@@ -9,8 +9,8 @@
  */
 
 SELECT getdatabaseencoding() <> 'UTF8' OR
-       current_setting('lc_ctype') = 'C' OR
-       (SELECT datlocprovider='i' FROM pg_database
+       (SELECT (datlocprovider = 'c' AND datctype = 'C') OR datlocprovider = 'i'
+        FROM pg_database
         WHERE datname=current_database())
        AS skip_test \gset
 \if :skip_test