Redundancy in `dash::HBWSpace::check_hbw_available`

[bertwesarg]

This function takes the result of dash::util::DashConfig.avail_memkind and DASH_ENABLE_MEMKIND as inputs for its decision. Though, dash::util::DashConfig.avail_memkind itself is based on @CONF_AVAIL_MEMKIND@ which is set in dash/CMakeLists.txt based on ENABLE_MEMKIND and MEMKIND_FOUND. But in the same place -DDASH_ENABLE_MEMKIND is added to the compile flags. Thus booth inputs results from the same CMake variables. Making them redundant.