Allocating array instances should be confined to ObjArray::allocate_instance and it's only callers in oopFactory and deoptimization.

InstanceKlass::allocate_objArray duplicates this functionality and calls heap array_allocate directly and its only caller is oopFactory. So it should be removed.

This reconciles differences in the valhalla repo where arrays have been reworked to handle flattened arrays of inline/value types.