I know nothing of the Harmony remote but I use a Hauppauge remote and it does what I think that you are after. I can delete a single recording by pressing the "Record" button on the remote when I am in, for example, "What's New".
I can also delete all recordings in a "group" under "Ready" by selecting the "group" and pressing the "Record" button. I suspect that the "Record" button maps to Ctrl+K on the keyboard. Does Ctrl+K do what you want?
AMD A75, 4 Gig, 1000 Gig, Nvidia N210
1 x Hauppauge WinTV QuadHD DVB-T2
1 x TBS 6281 dual DVB-T2
2 x Hauppauge Nova-t PCI