MAINT Remove unused plot_volume_per_day_hist.
MAINT Remove unused plot_volume_per_day_hist.

r0k3/pyfolio,sketchytechky/pyfolio,r0k3/pyfolio,femtotrader/pyfolio,quantopian/pyfolio,ChinaQuants/pyfolio,ChinaQuants/pyfolio,YihaoLu/pyfolio,YihaoLu/pyfolio,dursk/pyfolio,dursk/pyfolio,chayapan/pyfolio,sketchytechky/pyfolio,femtotrader/pyfolio,quantopian/pyfolio