There has never been an option to reset the default scale.
You can use a smaller brush (1,5-2,5) with Randomize activated, a Value of 0,85 and 0,0 Falloff to restore the scale in the editor. It's not the same but very close and from what I can tell it's absolutely sufficient.
If you want to restore the scale 1:1 you have to open the dstr_dstrname.tga with PhotoShop or Gimp and edit the green channel- exchange the channel with one from an unchanged dstr_.tga.
May I ask why you need to reset the scale? What's the problem?