clean up GenerateBlock()
clean up GenerateBlock()

mharkus/Sia,mtlynch/Sia,johnathanhowell/Sia,mtlynch/Sia,NebulousLabs/Sia,rivine/rivine,mnsl/Sia,MrStrong/Sia,ericflo/Sia,ericflo/Sia,Mingling94/Sia,MrStrong/Sia,cyrozap/Sia,NebulousLabs/Sia,mharkus/Sia,ChrisSchinnerl/Sia,rivine/rivine,ChrisSchinnerl/Sia,kustomzone/Sia,mnsl/Sia