The code I pointed out earlier is the code that facilitates the functionality your missing. You need to check and make sure it is in the correct position in your code. If your code is modified, it would not necessarily be the same line number. If you check the delete image box and save, and the image is still there, this is the code that does it.
When this works correctly, you will see the images you are trying to delete on the confirmation page. But once you submit the confirmation page, the block of code starting at line 230 will remove those images and the references in the database.
I think I owe you a huge apology, I was being premature in assuming that the images were not being deleted. As you said they show on the confirmation page but after clicking update they are in fact deleted with one exception. This does not work for the first image titled "Products Image" above "Products Image1". This file does not delete but can be replaced by selecting another image.
Another quirk I have come across is that if my image name contains the character ' then the image will not save properly and be displayed in my product page. In fact it turns out that on my server a file gets uploaded with a strange filename. For example if I try to upload King's.gif then the image does not work and what appears on the server is a file named King\'s.gif. this file cannot be deleted, renamed or moved. I have to go to my host control panel to delete it. Of course the simple fix is to rename the files before selecting them which is really not an issue.
Please remember I am not complaining, I am just letting you know about 2 quirks I have run across. Neither of which changes the fact that I could not have my site as I want it without your great piece of work.