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

Affects: Server-7.1   —   Status: Complete   —   Priority: Medium

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

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.