Content ads box checked = show up on AdSense Search box checked = show up on non-Google search network
Google search is not uncheckable, but...
You can bid at least 1c lower on the campaigns where you have checked content. Then only the ones in the other campaign (the one where you have checked search and that you want to display on Google search) will show on Google search.
This will give you one campaign that displays on Google search and search network, and a second campaign that displays on the content network only.