[flang][NFC] Deallocation of polymorphoc entities are done with the runtime call

The runtime function `AllocatableDeallocate/PointerDeallocate` is reponsible to
deallocate and finalize it. This patch just adds tests to make sure the correct
runtime function is called.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D137068