Remove useless comments.

include/mruby/string.h

@@ -46,7 +46,7 @@ void mrb_str_concat(mrb_state*, mrb_value, mrb_value);
 mrb_value mrb_str_plus(mrb_state*, mrb_value, mrb_value);
 mrb_value mrb_ptr_to_str(mrb_state *, void *);
 mrb_value mrb_obj_as_string(mrb_state *mrb, mrb_value obj);
-mrb_value mrb_str_resize(mrb_state *mrb, mrb_value str, int len); /* mrb_str_resize */
+mrb_value mrb_str_resize(mrb_state *mrb, mrb_value str, int len);
 mrb_value mrb_str_substr(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len);
 mrb_value mrb_check_string_type(mrb_state *mrb, mrb_value str);
 mrb_value mrb_str_buf_new(mrb_state *mrb, int capa);
@@ -55,7 +55,7 @@ mrb_value mrb_str_buf_cat(mrb_state *mrb, mrb_value str, const char *ptr, size_t
 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_str_dup */
+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_cat_cstr(mrb_state *, mrb_value, const char *);
 mrb_value mrb_str_to_inum(mrb_state *mrb, mrb_value str, int base, int badcheck);