To preventing from instantiating an abstract class, hiding its constructor is enough. Moving destructor to public doesn't break this intention. This also makes us can use smart pointer to manage derived Port class. Change-Id: Ic9cf97e90a6c26108d359eb459df48cd23eaf15c Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23925 Reviewed-by: Gabe Black <gabeblack@google.com> Maintainer: Gabe Black <gabeblack@google.com> Tested-by: kokoro <noreply+kokoro@google.com>