WL#1685: optimize update/delete when we don't have to read old row

We should optimize DELETE/UPDATE to not read rows before doing the delete/update
for some trivial but common DELETE/UPDATE statements.

This allows NDB to do some operations more efficently

This could also help to fix bugs or unnecessary deadlocks in InnoDB
INSERT…ON DUPLICATE KEY UPDATE.

This might also be useful for WL#148 ON (UPDATE|DELETE) (CASCADE|SET NULL).

See also WL#2442: Batched operation of multi UPDATE statements


This has already been implemented in MySQL Server, it's called rbwr(read before 
write removal). This WL is most likely a duplicate or has been resurrected.. a 
scary zombie.