I believe Kovid has been requested in the past for a way to delete the history in this and other boxes, e.g. Searchbar, S&R, etc.
But it is a low-priority thing, since most people don't care, the ones who do are usually comfortable editing the config data manually, and apparently implementing a delete feature is non-trivial (as in, he can't just change a setting, it would have to actually *be implemented*).
I'm sure if it were a more common need, it would be added.
