When trying to open the table to delete from, single-table DELETE
ignores CTEs, which thus violates SQL's name visibility rules.
That's because it calls add_table_to_list() with parse_context==nullptr,
which has the effect that adding the table-to-delete doesn't
search in the WITH clause to see if it is a CTE, as the WITH clause
is accessible from parse_context.
Fix: set the parse_context argument. I have gone through all calls
to add_table_to_list(pc=nullptr) in all types of SQL statements,
and I think only this call needs fixing.

Reviewed-by: Gleb Shchepa <gleb.shchepa@oracle.com>
Change-Id: Iea3167adf861618bd6b351fa164057cf102c78e9