SOFTWARE-6275 Remove retired IGWN CVMFS repos

[jasoncpatton]

Per @josh-willis (many moons ago), these repos are retired:

/cvmfs/ligo.storage.igwn.org/
/cvmfs/shared.storage.igwn.org/
/cvmfs/virgo.storage.igwn.org/
/cvmfs/kagra.storage.igwn.org/
/cvmfs/ligo-test.storage.igwn.org/

I believe these are covered under the two OASISRepoURLs removed here.

(/cvmfs/software.igwn.org/ and /cvmfs/gwosc.osgstorage.org/ should remain, which I believe are served by the other two URLs)

OSG SOFTWARE Jira link