Quickest way to delete unused templates in Oracle APEX

Best practice is to remove unused/unwanted templates from your application.
This encourages standardization in your application, which benefits both your users and developers.
It also reduces the size of your application.

But how to do it quickly?
APEX deliberately makes you delete them one at a time, a reasonable sanity check for novices.
But not very helpful if you know exactly what you want.

So here's how:

1. Export the theme
2. Use the splitter utility following instructions in apex/utilities/readme.txt
3. Comment out the unwanted templates as shown above 
4. Import the theme from the sql command line.

And best of all, it's iterative, so you can repeat it as often as needed!

Note: It's not the quickest way -  but it is the quickest supported way.