Removed incomplete vp2hdf_diff tool. Direct comparison between compressed files currently works if the same compression method has been used

Removed duplicate source file in CubismApps/Compressor.  The source file in
tools/reader is the main file.
The library related files use only the MPI C-bibdings. Some applications in
tools still used C++ MPI bindings. This will be fixed later

This source file is part of the CubismApps/tools directory.  It has not been
updated there as CubismZ will replace the reader used in the CUBISM-MPCF
repository in the future

Taken from SHA 3856b4d86757938f73638843c5ab63ad0bd5ba53

The Cubism source is maintained in a separate repository.  If you clone the
CubismZ repository, you need to setup the submodule as follows:

git submodule init
git submodule update

done.