cd C:\Program Files (x86)\osu!\songs
del /s *.avi
del /s *.flv
del /s *.wmv
del /s *.mp4 

ScreenShots of osu!vd
http://imgur.com/a/YWOP9

Would be cool if you could chose the path of your osu! Songs folder

As a fair warning, this may or may not cause all maps with videos to become unranked and require reing when osz2 comes out in the distant future. Use at your own risk.

just video should be fine in all cases, as it is optional.

Can't you just click novideo when going to ?

Not retroactively. Also, the beatmap packs contain video by default.