remove `mrb_str_offset`

include/mruby/string.h

@@ -69,7 +69,6 @@ mrb_value mrb_str_buf_new(mrb_state *mrb, size_t capa);
 
 char *mrb_string_value_cstr(mrb_state *mrb, mrb_value *ptr);
 char *mrb_string_value_ptr(mrb_state *mrb, mrb_value ptr);
-int mrb_str_offset(mrb_state *mrb, mrb_value str, int pos);
 mrb_value mrb_str_dup(mrb_state *mrb, mrb_value str);
 mrb_value mrb_str_intern(mrb_state *mrb, mrb_value self);
 mrb_value mrb_str_to_inum(mrb_state *mrb, mrb_value str, mrb_int base, mrb_bool badcheck);

src/string.c

@@ -162,13 +162,6 @@ mrb_str_resize(mrb_state *mrb, mrb_value str, mrb_int len)
 
 #define mrb_obj_alloc_string(mrb) ((struct RString*)mrb_obj_alloc((mrb), MRB_TT_STRING, (mrb)->string_class))
 
-/* char offset to byte offset */
-int
-mrb_str_offset(mrb_state *mrb, mrb_value str, int pos)
-{
-  return pos;
-}
-
 static struct RString*
 str_new(mrb_state *mrb, const char *p, size_t len)
 {