Figured this out myself eventually. Posting the solution here in case anyone ends up here searching for this situation.
My confusion came from the installation location. I guess a 32-bit installation of Photoshop CC went into "c:\program files (x86)\", but the one I was working off of was in "c:\program files\".
I tracked down all the files in the "plug-ins" directories there and removed them, which did the trick.
