Remove cmake from NCEPLIBS-external

[edwardhartnett]

The NOAA HPC systems will use hpc-stack to install software, not NCEPLIBS-external. But it still has a place for external users.

However, it needs to be trimmed back to just those packages that don't have their own install mechanisms. CMake is already well-understood and can be installed anywhere. Instead of providing it, we can just require it.