The odd thing is that it does not seem to exist any more not even a note to say it is depreciated?
The old links point to main Google code site. If I look at the list of API's on that site the API it replaced is there Web Search API (Deprecated) which links back to same page but not the Google AJAX Search API.
Further Google searching is not being helpful either, many blog posts pointing to the same Google site (http://code.google.com/apis/ajaxsearch/) that has no content and redirects to the same place?
Just to prove it did exist I have found it on the way back machine however the last snapshot did not show any special unusual message.