[Cleanup] Remove unused variables in miner
[Cleanup] Remove unused variables in miner

remove:
- nLastCoinStakeSearchTime (and nSearchTime/fStakeFound + if block)
- fLastLoopOrphan
PIVX-Project/PIVX,Mrs-X/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX