bpo-41654: Fix deallocator of MemoryError to account for subclasses (GH-22020)

bpo-41654: Fix deallocator of MemoryError to account for subclasses (GH-22020)

When allocating MemoryError classes, there is some logic to use
pre-allocated instances in a freelist only if the type that is being
allocated is not a subclass of MemoryError. Unfortunately in the
destructor this logic is not present so the freelist is altered even
with subclasses of MemoryError.