sql: remove field suppressErr from struct sql

The suppressErr field was used to indicate that most of the errors
during the parsing should be suppressed. There was only one
feature that used it. After deleting this feature, it became
obvious that this field had become unused and should be removed.

The feature in question is: allow to use names and aliases from
input in ORDER BY clause of UNION or INTERSECT. After deleting
of this feature, requests like the one below become invalid:

SELECT 1 AS a UNION ALL SELECT 2 AS b ORDER BY b;

Part of #3965