CI is currently installing netCDF and MPICH, but neither are used

[edwardhartnett]

In our CI we have:

        sudo apt-get update &> /dev/null
        sudo apt-get install libmpich-dev
        sudo apt-get install libnetcdf-dev libnetcdff-dev netcdf-bin pkg-config
        sudo apt-get install libpng-dev
        sudo apt-get install libjpeg-dev doxygen
        python3 -m pip install gcovr

We don't need netCDF or MPICH so these can be removed.