NFSv4.1: Comment is now wrong and redundant to code

The save of the write offset was removed some time ago, so that
part of the comment is bogus.

The remainder is pretty self-evident.

So off with it!

Signed-off-by: Tom Haynes <Thomas.Haynes@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>