My take is that answer was how to not allow uploading of any files with a given extension. This question is how to allow images in posts, but instead of having - icon, modal - drag, drop - copy, paste - type URL - not have the icon, modal as a way to put images in posts regardless of extension.
To be clear, it is not that you want to make it impossible for members to insert images from their computer, only to hide that one particular option and make it perhaps a bit more difficult to do.
If so, CSS should be easy enough once an appropriate selector is determined.