Trim unnecessary config.h defines from prerequisite list

The lists in opm-*-prereqs.cmake contained a lot of variables that were not in any header file in the modules. Granted, many of these variables are pulled in by the DUNE-modules anyway, but that doesn't mean they belong in the prerequisite list for those modules anyway (the lists aren't transitive -- each module should only declare what itself need).

This changeset prunes the list down to what is actually needed. Note that variables needed only by opm/*.c* files should rather go in CMakeLists.txt, so they are not propagated to other libraries.