remove redefinition of MB_CUR_MAX in locale_impl.h

unless/until the byte-based C locale is implemented, defining
MB_CUR_MAX to 1 in the C locale is wrong. no internal code currently
uses the MB_CUR_MAX macro, but having it defined inconsistently is
error-prone. applications get the value from stdlib.h and were
unaffected.

src/internal/locale_impl.h

@@ -30,6 +30,3 @@ const char *__lctrans_cur(const char *);
 #define CURRENT_LOCALE (__pthread_self()->locale)
 
 #define CURRENT_UTF8 (!!__pthread_self()->locale->cat[LC_CTYPE])
-
-#undef MB_CUR_MAX
-#define MB_CUR_MAX (CURRENT_UTF8 ? 4 : 1)