Removes unused date_to_datetime in zipline.
Removes unused date_to_datetime in zipline.

dmitriz/zipline,ronalcc/zipline,keir-rex/zipline,mattcaldwell/zipline,euri10/zipline,iamkingmaker/zipline,CDSFinance/zipline,joequant/zipline,quantopian/zipline,wubr2000/zipline,umuzungu/zipline,davidastephens/zipline,michaeljohnbennett/zipline,alphaBenj/zipline,sketchytechky/zipline,dhruvparamhans/zipline,mattcaldwell/zipline,morrisonwudi/zipline,bartosh/zipline,florentchandelier/zipline,cmorgan/zipline,jordancheah/zipline,wubr2000/zipline,wilsonkichoi/zipline,chrjxj/zipline,gwulfs/zipline,StratsOn/zipline,euri10/zipline,humdings/zipline,erikness/AlephOne,cmorgan/zipline,semio/zipline,quantopian/zipline,umuzungu/zipline,MonoCloud/zipline,CDSFinance/zipline,iamkingmaker/zipline,CarterBain/AlephNull,nborggren/zipline,aajtodd/zipline,Scapogo/zipline,chrjxj/zipline,grundgruen/zipline,sketchytechky/zipline,davidastephens/zipline,dmitriz/zipline,ChinaQuants/zipline,morrisonwudi/zipline,wilsonkichoi/zipline,zhoulingjun/zipline,keir-rex/zipline,humdings/zipline,MonoCloud/zipline,DVegaCapital/zipline,otmaneJai/Zipline,aajtodd/zipline,Scapogo/zipline,joequant/zipline,jimgoo/zipline-fork,stkubr/zipline,kmather73/zipline,dhruvparamhans/zipline,CarterBain/AlephNull,bartosh/zipline,AlirezaShahabi/zipline,florentchandelier/zipline,AlirezaShahabi/zipline,dkushner/zipline,DVegaCapital/zipline,enigmampc/catalyst,ronalcc/zipline,StratsOn/zipline,dkushner/zipline,zhoulingjun/zipline,YuepengGuo/zipline,semio/zipline,michaeljohnbennett/zipline,ChinaQuants/zipline,alphaBenj/zipline,grundgruen/zipline,erikness/AlephOne,magne-max/zipline-ja,enigmampc/catalyst,otmaneJai/Zipline,nborggren/zipline,magne-max/zipline-ja,jimgoo/zipline-fork,jordancheah/zipline,YuepengGuo/zipline,stkubr/zipline,gwulfs/zipline,kmather73/zipline