You CAN just pull them from the PXE server. Find the folder - delete - restart PXE. What would be really interesting is if they come BACK.
PXE in 7.5 doesn't read an INI file from the server to know what PXE menu options to display - it simply enumerates the folders available. SO - remove the folders, and voila - options gone.
That said, IF the NS thinks those menu's SHOULD be there, they'll rebuild. In theory. IF they do rebuild, that would be really fascinating.
If you only have a single PXE server, just delete the sub foler for the options you don't want there (assuming they're "gone" in the console) an then restart the PXE server service. That shoul pull the option. If so, wait say 24/48 hrs and see if it returns.
Then let us know.
That's not a "fancy" answer, but it should be better than no answer at all. :P