Remove FindCUDAToolkit backport

In 3f66927, `FindCUDAToolkit.cmake` was backported from CMake 3.31
to get
https://gitlab.kitware.com/cmake/cmake/-/commit/b38a8e77cb3c8401b3022a68f07a4fd77b290524,
which was introduced in CMake 3.28. Since we now require CMake 3.30,
we no longer need the backport.