I tried going to help ->install new software -> check what's already installed... The uninstall option is grayed out for all the relevant plugins. No indication whatsoever why, or how to fix this.
I instead try going to Help-> Check for New updates. It simply pops up a dialog saying no updates were found. No further options.
I try going to Help-> Eclipse marketplace. It seems Solutions (which are the only things you can modify using this dialog) are different than plugins.
I try going to Help->about eclipse ->installation details. I get the same menu as if I click install new software.
I try googling. It either says go to Help->about eclipse ->installation details (which I already tried), or to do Help -> Software Updates -> Manage Configuration. The second suggestion is simply not available on Eclipse Helios. I assume I am looking at the documentation for a different version of eclipse. I find the documentation for Eclipse Helios (3.6), and nope, it's exactly the same. At this point I hit a lucky break, and I notice that the text describing the menus to open is a link. I click on it and it says "you can only do this with local help". I find the same page again in the local eclipse help. I click the link. Viola, the magical hidden window pops up that finally allows me do uninstall the plugins. Did it really have to be that hard?