Okay. I am not sure if I was clear enough when I referred to it as a "panel box". The correct term to what I was referring is the Discover 'thumbnail' that was added to the Speed Dial in Opera 30. It is an active thumbnail on the Speed Dial that displays a cycle of news stories.
I am completely satisfied to leave the Discover link that is at the bottom of the Speed Dial (which sits along with History, etc). It is a nice feature to use WHEN I want to use it. Even if I did not like the Discover link, there is not a way to remove that. So, yes, there is not a way to remove the Discover feature in Opera, but there is a way to remove the Discover thumbnail on the Speed Dial.
I myself was able to remove the Discover thumbnail on the Speed Dial by disabling Experimental Start Page option on Opera:Flags. Maybe it will not work for everyone, but it certainly worked for me. However, this was on a Windows 7 computer with a fresh install of Opera 30 (no previous versions).
Interestingly, another computer with Windows Vista and previous installations of Opera did not have the Discover thumbnail at all and still had Experimental Start Page selected. So I am not entirely sure if every version of Opera 30 is on the same page, so to speak.
Out of curiosity, Airforce, do you have the Discover thumbnail in your Speed Dial (it's slightly larger than other thumbnails and permanently to the left of them)? Unlike other thumbnails, like a thumbnail created for ReadWriteWeb, you can't click X to remove it. I wanted to remove it because I like to have my speed dial contain what I want and not see roving headlines of some latest murderer's horror show along with random other headlines. But like I said, the Discover feature itself which can be accessed from a neutral link at the bottom of the Speed Dial is nice WHEN I can choose to use it.
Maybe that's petty, but I like Opera and was surprised to see it stick this feature right into my Speed Dial with no way to X it. I already see enough news every day. Enough grim, tabloid headlines. Ideally Opera should have made it optional and allow one to just X it from the Dial.