Removing PCB sets/bioses from MAME menu?

[Escape-To-88]

I use an older version of MAME I have set-up nicely and I use a front-end, rather than use MAMEGUI.

As you can see from the screenshot however I can't remove certain PCB details from the list. I can't 'remove from list' in option, nor can I 'add to custom folders' - just wondered if I can remove them from view? (Basically all the read bits on here)
Cheers.
PIC:

MAME Query.jpg