Fix speed problem in n3fit

Created by: scarlehoff

Many thanks @tgiani for the tip

Apparently the fix for 2.2 I did in #718 was destroying the speed of n3fit. This commit basically reverts that. The most dangerous two lines ever written :P

I'll investigate on how to simultaneous be compatible with 2.2 and have the same speed but for now I don't think we have to worry, TF just pushed a 4th release candidate for 2.2, I think also them are having some trouble.

/cc @scarrazza @RoyStegeman if you are running things that depend on speed, it would be good for you to get this fix. For now I've only tried a DIS fit but the speed went down by a factor of 4 (i.e., back to the numbers I had before). I'm running a replica for a Global fit to see how it does with that.