Remove isascii_l(3).

Had intended to remove this one before submitting the locale changes,
but forgot. It isn't a standard ctype function, so we don't need it.

Change-Id: Ie9c09fa6c61b1101b5992fa06da30e373a0c6bf7

libc/include/ctype.h

@@ -75,7 +75,6 @@ int	toupper(int);
 
 int isalnum_l(int, locale_t);
 int isalpha_l(int, locale_t);
-int isascii_l(int, locale_t);
 int isblank_l(int, locale_t);
 int iscntrl_l(int, locale_t);
 int isdigit_l(int, locale_t);