Disable build kluge that is no longer pertinent

The <have_boost_redef.hpp> header was introduced (commit
OPM/opm-core@82369f9) as a work-around for a particular interaction
in the Autotools-based setup of OPM-Core and the Dune core modules.
Notably, Dune's "Enable" trick for Boost failed on some older
Autoconf systems.  Now that we're using CMake, however, that kluge
is no longer needed because OPM-Core always

  #define HAVE_BOOST 1

i.e., as an explict true/false value.

Therefore, we need no longer include <have_boost_redef.hpp> .  The
header will be removed at a later time.