This is a bit of an issue for Nick's calibration work, since it typically involves data with labeled reference standards. The lack of this feature makes it impossible to remove a peak with the peptide selected. Instead, you need to select a precursor and remove the peak.

Example data can be found at:

https://panoramaweb.org/labkey/targetedms/Panorama%20Public/2015/Schilling%20-%20main_Study_9/Study_9.2_CalCurves/showPrecursorList.view?id=1165