ink_utf8_to_latin1 is not defined, removing declaration (#7737)

Author: bryancall

include/tscore/ink_string.h

@@ -76,9 +76,6 @@ size_t ink_strlcpy(char *dst, const char *str, size_t siz);
 size_t ink_strlcat(char *dst, const char *str, size_t siz);
 #endif
 
-/* Convert from UTF-8 to latin-1/iso-8859-1.  This can be lossy. */
-void ink_utf8_to_latin1(const char *in, int inlen, char *out, int *outlen);
-
 /*===========================================================================*
 
                              Inline Functions