Mk/bsd.sites.mk: Remove stale sites
- https://cran.cnr.berkeley.edu/ looks like is no more active as it serves with default apache page
- https://ftp.mirrorservice.org/sites/ftp.netlib.org/ no longer serves this specific SUBDIR
- https://www.mirrorservice.org/sites/ftp.netlib.org/ no longer serves this specific SUBDIR
- https://mirror.nl.leaseweb.net/xorg/%SUBDIR%/ no longer serves this specific SUBDIR
Approved by: portmgr (blanket)