As far as I'm aware there's no way to remove that line - and it would be a very confusing event log if it were removed, as you wouldn't know when any particular event happened.
If you are having trouble with visually distinguishing the events, you can change the colours of various events by clicking some of the buttons on the bottom of the window. This may help you when scrolling back through it.
I'll also say that, in a few years of in-game time, you likely won't have this issue anymore - each day will generate enough events that the "last increment" entries will be a small proportion of them.
