Right-click in the left-most area (where the track numbers and icons are) and choose Remove Empty Tracks, although that seems to work better for empty tracks below the last used track. BTW it always leaves on empty track at the bottom

The manual approach would be to select all the content (Ctrl+A) and move everything up one track so your video(s) is(are) on Track 1. You could then select all your photos and move them to Track 2 and then use Remove Empty tracks.

It's obviously better to use plan your use of tracks from the beginning, but there's also no harm in having any number of empty tracks