I would always be in favor of removing all such libraries on the DRY principle. To do otherwise suggests that the newer SRFI depends on some specific (possibly outdated) version of the older SRFI's code. People who have access to a SRFI should be assumed to have access to all SRFIs, at least those with portable implementations.
I'm inclined to agree with John about this. Deleting copies makes it less likely that people will end up spending time tracking down this kind of problem.
I'll wait a few more days, but unless anyone objects, I'll remove the copies and add a README file that points people to the canonical sources of the required SRFIs.