The easiest way to learn what files are relevant is to open up a slider-only theme in iFile that you know works--they have a lot fewer files to dig through than a full bundled theme, so it simplifies things a lot. Then just find those same files in your current theme--you can either rename them or remove them altogether. I usually just put an asterisk in front of the file name, that's enough to disable it, but it means I don't have to re-download an entire theme if I change my mind later on. Disabling all the relevant files (they should all be pngs, but may be in different locations) should bring back the original slider for you.
File names do often change from one iOS version to another, so make sure to look at a slider theme you're certain works on your current phone/iOS.
