Delete a TFC override that uses the old dcap at FNAL and update FNAL storage plugin for unmerged files in backfill

We have to test this though. The failure was found on tier0 wmagent jobs, but it really sounds like we should have noticed this problem before... dcap is not used anymore at FNAL since disk tape separation (several months ago). Using the default config for FNAL should be enough. I checked with Catalin and we need to update the FNAL storage plugin.