feat: proper exports implemented for C++ modules

test/static/reference_test.cpp

@@ -21,9 +21,6 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
@@ -31,7 +28,6 @@ import mp_units;
 #include <mp-units/system_reference.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/unit.h>
-#endif
 
 namespace {