[PoS] Allign ComputeStakeModifier (v2) to nHeight logic
[PoS] Allign ComputeStakeModifier (v2) to nHeight logic

[PoS] cleaning not used stakeTargetHit method + fixing bad nHeight in
the new compute modifier method.

Darknet-Crypto/Darknet,Mrs-X/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX