RF: Simplify sparse NNLS fitting a bit more.
RF: Simplify sparse NNLS fitting a bit more.

Messaoud-Boudjada/dipy,Messaoud-Boudjada/dipy,oesteban/dipy,JohnGriffiths/dipy,FrancoisRheaultUS/dipy,sinkpoint/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,sinkpoint/dipy,JohnGriffiths/dipy,mdesco/dipy,jyeatman/dipy,StongeEtienne/dipy,villalonreina/dipy,matthieudumont/dipy,beni55/dipy,jyeatman/dipy,oesteban/dipy,demianw/dipy,nilgoyyou/dipy,nilgoyyou/dipy,rfdougherty/dipy,demianw/dipy,beni55/dipy,matthieudumont/dipy,StongeEtienne/dipy,mdesco/dipy,rfdougherty/dipy