Deleting it from the table will NOT delete it from PXE.
To remove it from the PXE menu it needs to be pulled from the console, AND that removal must be executed client-side. All it does when executed is to essentially delete the sub-folder under Images and cycle PXE so if you wanted to do so yourself, you could remove the image and ... cycle the PXE services.
In 7.5. The same does NOT apply to 7.1.
In 7.5, if you review the pxe logs, you'll literally see it enumerate the folders and build a menu from them. Translation - you can add your own by dropping in a folder, and remove one by pulling out a folder. That's all there is to it.