Remove pg_regex_collation
We can also use the existing pg_regex_locale as the cache key, which
is the only use of this variable.
Reviewed-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://www.postgresql.org/message-id/flat/
b1b92ae1-2e06-4619-a87a-
4b4858e547ec%40eisentraut.org