Remove pg_authid's TOAST table.

Remove pg_authid's TOAST table.

pg_authid's only varlena column is rolpassword, which unfortunately
cannot be de-TOASTed during authentication because we haven't
selected a database yet and cannot read pg_class.  By removing
pg_authid's TOAST table, attempts to set password hashes that
require out-of-line storage will fail with a "row is too big"
error instead.  We may want to provide a more user-friendly error
in the future, but for now let's just remove the useless TOAST
table.

Bumps catversion.

Reported-by: Alexander Lakhin
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/89e8649c-eb74-db25-7945-6d6b23992394%40gmail.com