Undo changes from 4998b114e that break existing MSVC build

This defines should be in common header file and wrapped
in an #ifndef clause

libs/pbd/cartesian.cc

@@ -15,9 +15,6 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#ifdef COMPILER_MSVC
-#define _USE_MATH_DEFINES
-#endif
 
 #include <math.h>
 

libs/pbd/windows_special_dirs.cc

@@ -23,10 +23,6 @@
 
 #include "pbd/windows_special_dirs.h"
 
-#if defined (COMPILER_MSVC) && !defined (PATH_MAX)
-#define PATH_MAX _MAX_PATH
-#endif
-
 std::string
 PBD::get_win_special_folder_path (int csidl)
 {