Well, it's in the FORUMHOME template. And it's marked with comments. So you could go to admincp > stylemanager > select style > edit templates.
Then look for "Forum Home Templates." Expand that and you'll see the "FORUMHOME" template. The what's going on box is marked with comments so you'd remove everything between and including "<!-- what's going on box -->" and <!-- end what's going on box -->.
I've never tried that though, so you might want to test it first. Or wait for somebody else to confirm. But that's where the code is at.
EDIT: I'm slow. Outbackmark 1, mme42 0.