Revert "DUNE/IMC: merged definitions from LSTS/imc@52d0d4951e43322e9b6acf960641071d4a41f417"

This reverts commit 8c36d12c69ef9d3236da81b55ce246ad31c9283f.
Revert "DUNE/IMC: Upped version to 5.5.x to reflect upstream (LSTS/imc@0f49709ad61157fa2d14f3710d4c41f0345ac91e)."

This reverts commit f67465a61bea5129b459a07ab33d7fee5d2516ae.

Conflicts:
	programs/tests/test_IMC.cpp
	src/DUNE/IMC/Blob.cpp
	src/DUNE/IMC/Constants.hpp