Have you tried to remove it from the settings of the Fallout visualization itself?  That's where I remove it when I use this type of report and it always works for me. 

I'm having issues getting the histogram visualization to deliver results that make sense.I created a histogram in Workspace looking for a distribution of Page Views per Unique Visitor and applied a segment to the panel to limit the page to only the single page I'm interested in.  My segment is a hit...