db-ctl-base: Drop redundant 'table' field from struct ctl_row_id.

db-ctl-base: Drop redundant 'table' field from struct ctl_row_id.

The 'table' field is redundant because the required 'column' field
implies the table that the column is a part of.

This simplifies the users and makes it harder to get these things wrong.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Andy Zhou <azhou@ovn.org>