alias f1 if ($active == status window) clear
I wouldn't override f1 though, as that is the shortcut to your help file. Don't forget you can use control (cf<number>) and shift (sf<number>) so that gives you a lot of choice for a key combination.
Alternatively you could use:
f1 clear -s
Now it will clear the status window, if you issue f1 on any window that is part of a certain server. In other words, if your active window is a channel, and you press f1, it will clear the status window from the server where this channel is in.