It may depend on what version of ViPR SRM you are using. However, in 3.7.1, if you edit the report, in the Report Library, that you have previously scheduled and navigate to the the Report Details tab you can set the Legend Visibility value to "visible only in the default display" then the emailed report does not show the legend when it is generated.
I have some reports "pinned" to personal views to create custom dashboards, and then schedule these as .pdf email reports. I can turn the legends on/off in the view, but can't figure out how to retain these when they are mailed out.
Display legends on personal view / scheduled reports?