lib/libc/string0: Remove better-than-standard strncpy() implementation.

ANSI C doesn't require that strncpy() produced null-terminated string, so
it's basicly useless for string manipulation.

lib/libc/string0.c

@@ -169,15 +169,6 @@ char *strcpy(char *dest, const char *src) {
     return dest;
 }
 
-char *strncpy(char *dest, const char *src, size_t dest_sz) {
-    char *d = dest;
-    while (*src && --dest_sz) {
-        *d++ = *src++;
-    }
-    *d = '\0';
-    return dest;
-}
-
 // needed because gcc optimises strcpy + strcat to this
 char *stpcpy(char *dest, const char *src) {
     while (*src) {