netdoc: Remove a TODO hs comment.

It said to check whether C enforces an absence of extraneous bytes
at the end of the link specifiers.  It does, in
`hs_desc.c:decode_link_specifiers()`, where it says:

```
  if (link_specifier_list_parse(&specs, decoded,
                                (size_t) decoded_len) < decoded_len) {
    goto err;
  }
```

The comparison with "decoded_len" checks whether all the bytes were
decoded.

crates/tor-netdoc/src/doc/hsdesc/inner.rs

@@ -166,7 +166,6 @@ impl HsDescInner {
                 let mut r = tor_bytes::Reader::from_slice(ls.as_bytes());
                 let n = r.take_u8()?;
                 let res = r.extract_n(n.into())?;
-                // TODO hs: Check whether c tor enforces that this field is exhausted.
                 r.should_be_exhausted()?;
                 res
             };