cleanup: Boost versions checks
According to https://gitlab.psi.ch/OPAL/src/wikis/For-Developers/Compile-OPAL boost version 1.66 is required.
However, in CMakeLists.txt the minimum version required is 1.60.
@gsell: which one is correct?
In the code there are a few checks on various boost versions (1.60 and 1.62). If 1.66 is indeed required then we can remove those checks, else just the ones for 1.60.