[libcxx] Remove a broken win32 locale function redirection

[mstorsjo]

Summary

One can't replace vsscanf(_l) with a sscanf(_l) that doesn't take a va_list.

This has been untouched since it was added in SVN r140728, so apparently it hasn't been used since. One reason for this mistake originally might have been that there was no _vsscanf_l until MSVC 2015.

Since it's unused, just remove this define.

libcxx/trunk/include/support/win32/locale_win32.h

 #define towupper_l _towupper_l
 #define towlower_l _towlower_l
 #if defined(__MINGW32__) && __MSVCRT_VERSION__ < 0x0800
 #define strftime_l( __s, __l, __f, __tm, __loc ) strftime( __s, __l, __f, __tm )
 #else
 #define strftime_l _strftime_l
 #endif
 #define sscanf_l( __s, __l, __f, ...) _sscanf_l( __s, __f, __l, __VA_ARGS__ )
-#define vsscanf_l( __s, __l, __f, ...) _sscanf_l( __s, __f, __l, __VA_ARGS__ )
 #define sprintf_l( __s, __l, __f, ... ) _sprintf_l( __s, __f, __l, __VA_ARGS__ )
 #define vsprintf_l( __s, __l, __f, ... ) _vsprintf_l( __s, __f, __l, __VA_ARGS__ )
 #define vsnprintf_l( __s, __n, __l, __f, ... ) _vsnprintf_l( __s, __n, __f, __l, __VA_ARGS__ )
 _LIBCPP_FUNC_VIS int snprintf_l(char *ret, size_t n, locale_t loc, const char *format, ...);
 _LIBCPP_FUNC_VIS int asprintf_l( char **ret, locale_t loc, const char *format, ... );
 _LIBCPP_FUNC_VIS int vasprintf_l( char **ret, locale_t loc, const char *format, va_list ap );
 
 // not-so-pressing FIXME: use locale to determine blank characters