The robots.txt will not remove pages from the index. You've actually just told Google not to look at them, you haven't told them to remove them. You're better off using NOINDEX (and taking them out of robots.txt so that Google will actually see the NOINDEX) If you really want them out, remove them in GWT. THEN make sure there's no links to them, and put them back in robots.txt. At least, that's how I'd do it.