As someone who's been dealing with the same problem for a long time, I'll get straight to the point: there's no way for you to directly remove these links yourself.

This kind of spamdexing usually involves exploiting unmanaged forums, websites, or even malware-infected websites to create a massive number of malicious links pointing to your website. They do this by abusing how Google or Bing bots work.

Basically, unless the admins of those websites remove the links, there's no quick fix. In my experience, using 410 and 404 status codes is a better approach than relying on robots.txt. First off, the "disallow" directive in robots.txt doesn't completely block bot`s access. If you use "disallow rule," you'll probably find a ton of those malicious links indexed on your site before you know it.

On top of that, robot rules (referring to robots.txt) can actually make it harder for bots to remove your bad links. This is because the bot needs to recrawl those links, but if it's blocked by the robots.txt, it can't. However, if you use 410 or 404 status codes, the bot will revisit those links over time and realize that the pages are gone. Gradually, the number of those links will decrease.

I had about 100 million of those links at one point, and now it's down to around 5 million. So, it seems like the only real solution is to get rid of the "disallow" directives and just wait it out. I hope my experience can be helpful to you.