What was CPAN Ratings?

It was a very useful site where a user could rate (out of 5) and more importantly review CPAN modules.

Why isn't it there anymore?

An excellent question. There was never any concrete reason given for its demise AFAICR. The only rationale was in the NOC post which essentially suggests that the limited resources they have could be better used on other things than keep CPAN Ratings going. :-(

Do I need to do anything about it?

Just remove the link from the POD of your dist. You could always replace it with this one.