Remove K32 plots as K34 is ready to be moved

[FVierra27]

Thinking ahead here. I haven't plotted in many month at this point but it would be nice to plot a K34 and when it's ready delete some K32s and replace them.

[altendky]

This is an often requested item but I have been fairly hesitant to add deletion of plots to plotman. Any bug around that could be really bad. When I was replotting from OG to pooling plots I just deleted either a days worth of plots at a time or a disk worth. I know some other people did put together scripts for this and there are other discussions and issues around this, though I wasn't able to quickly find them.

[zorner]

#963 I just posted my approach.