Clean up MPP code

[underwoo]

Is your feature request related to a problem? Please describe. The code in MPP has many different paths, depending on the type of build: MPI, non-MPI, ShaMEM. The ShaMEM option has not been used in many years, and has likely not received required updates that were made in the MPI. The non-MPI build, at this time, is not possible. This is due to new template preprocessor macros not placed in the nocomm files.

Describe the solution you'd like MPP needs to be cleaned up to remove unused code, and combine as much code into fewer files as possible. The final version of MPP in libFMS should contain only build options that will be supported moving forward.

Describe alternatives you've considered None

Additional context This will modify many parts of MPP, and may be easier to deal with in smaller chunks. This issue can be used an epic issue.

• [ ] #306 - Remove shmem build configuration