Well I was thinking of adding it soon (so probably in r1.5 when it comes out) however if you'd like to just remove them from the perfdata graphs all together for right now... edit the file:
/usr/local/nagiosxi/html/includes/components/graphexplorer/templates/perfdata.inc.php
You should see the Highcharts code in there... from here it's pretty simple all you have to do is remove the legend:
Edit: I actually didn't realize but there is already a legend: { enabled: true } that you can change to false instead of enabled that will do what you want
Edit 2: I can confirm I have added the ability to remove the legend via a checkbox in the perfdata dashlet options when clicking the button on the perfdata page. It will be in 2014r1.5
Legend taking up too much space in HighCharts on Dashboard
Re: Legend taking up too much space in HighCharts on Dashboa
As of May 25th, 2018, all communications with Nagios Enterprises and its employees are covered under our new Privacy Policy.
Re: Legend taking up too much space in HighCharts on Dashboa
Great. Thanks!