Remove read-only server settings lc_collate and lc_ctype

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