There are several things you can do, in whatever combination you feel comfortable:
Downvote (the answer is incorrect, after all)
Leave a comment explaining why the answer is no longer correct/current
Edit the answer to be correct. (This can be tricky, though, as it may look to some like you're changing too much of the original)
Personally I go for 1 and 2. ...
I think you've done all you can do.
If it was just a question of some links being outdated, you could just edit the links. It doesn't seem that simple, though.
As there is another answer with the correct information, you can point people to that answer (which you've done).
The main complication is that the author of the original question no longer has an ...
You should not delete your answer. Just prepend with a last working date.
I find the idea of users searching around bothering people to delete time dependent answers cumbersome and useless.
Your answer gave value (and reputation) so keep it.
Is the "new" Google Spreadsheets universal? I'm not sure that it is. For those who are still stuck using (or refusing to update from) the old/original Google Spreadsheets your answer may still be useful.
Since it's not accepted, if you have determined that you can't edit it to be correct (at least, not without parroting the up-to-date answers), I guess the ...
I propose to have a more "impactful" (for the sake of lacking word) solution. Downvoting may not be sufficient if the existing upvote number is high, or it is accepted. A comment can be buried with the whole thread. Here are some suggestions:
A post notice
An edit at the top, saying it's obsolete
I think everyone should be allowed to do that.
I think we ...