[SYCL] Fix rule-of-three Coverity hit (#21267)
Coverity complains:
`sycl::detail::HostKernelRefBase` has a user definition for at least one
special function (copy constructor, copy assignment, destructor) but not
all. If one of these functions requires a user definition then the
others likely do as well.
This PR explicitly adds default destructor to `HostKernelRefBase`
