Remove obj handlers ptr value from spl_object_hash()

Remove obj handlers ptr value from spl_object_hash()

We still keep the same output length, for people who rely on the
return value having a specific format. The handler part will now
simply be always the same (it was the same nearly always anyway).

The motivation behind this change is to avoid breaking
spl_object_hash() and SplObjectStorage if an extension changes the
handlers table of an object. This has come up, for example, in
weakref implementations.