Remove bad cvsup mirrors:

• cvsup6.us.FreeBSD.org: Immediately closes connection
• cvsup8.FreeBSD.org/cvsup8.us.FreeBSD.org: Outdated (May 2013)
• cvsup2.dk.FreeBSD.org: Corrupt
• cvsup.fr.FreeBSD.org/cvsup1.fr.FreeBSD.org: "Invalid greeting from server"
• cvsup[3678].de.FreeBSD.org: No anonymous access (requires authentication)
• cvsup.gr.FreeBSD.org: Remove per r42137 (CNAME)
• cvsup.is.FreeBSD.org: Corrupt
• cvsup3.pl.FreeBSD.org: No longer carries FreeBSD repo
• cvsup3.es.FreeBSD.org: Outdated (Feb 2012)