Adjust bogus documentation.

src/mem.rs

@@ -1738,10 +1738,9 @@ pub fn convert_latin1_to_utf16(src: &[u8], dst: &mut [u16]) {
 ///
 /// # Safety
 ///
-/// Note that this function may write garbage beyond the number of bytes
-/// indicated by the return value, so using a `&mut str` interpreted as
-/// `&mut [u8]` as the destination is not safe. If you want to convert into
-/// a `&mut str`, use `convert_utf16_to_str()` instead of this function.
+/// If you want to convert into a `&mut str`, use
+/// `convert_utf16_to_str_partial()` instead of using this function
+/// together with the `unsafe` method `as_bytes_mut()` on `&mut str`.
 pub fn convert_latin1_to_utf8_partial(src: &[u8], dst: &mut [u8]) -> (usize, usize) {
     let src_len = src.len();
     let src_ptr = src.as_ptr();