Remove support for FreeBSD < 11.2 after FreeBSD 10.4 support ends (2018-11-01).
All ports that work only on FreeBSD 10 have already been marked DEPRECATED and
will be removed when they expire.
Some ports are not (fully) covered in this patch:
- ports-mgmt/poudriere[-devel] -> build ports on an old system (*)
- lang/perl5.26 -> required by ports-mgmt/poudriere-devel
- any patch in files/
Tools/scripts/tindex is untouched by this patch.
(*) Mk/bsd.port.mk does include a patch to raise the minimum supported version
to 11.2 though.