Remove FindNetcdf and FindPIO files

[anton-seaice]

@SeanBryan51 has added exports to the ParallelIO cmake, see NCAR/ParallelIO#2012. This should be in the next release (e.g. >2.6.6 )

So, in the access3 packages (share, mom6, cice, ww3) we should be able to remove FindPIO.cmake files.

In addition, we may be able to remove the FindNetCDF.cmake files and use pkgconf, e.g.:

something like this:

  if (NOT NetCDF_Fortran_FOUND)
    include(FindPkgConfig)
    pkg_check_modules(NetCDF_Fortran REQUIRED IMPORTED_TARGET "netcdf-fortran")
  endif()

[SeanBryan51]

[Probably outside the scope of this issue]

Just noting that NetCDF Fortran also supports installing CMake package config files.

However when we build NetCDF Fortran with spack, the CMake package config file is not installed since the spack package does not support the CMake build.

As pointed out by @anton-seaice, the NetCDF C spack build has the option for both CMake and Autotools, maybe it could be a useful contribution to do the same for NetCDF Fortran spack build