Remove cross compiled libraries for CloudABI.
These libraries are now provided by the CloudABI Ports collection -- not
just for FreeBSD, but a number of other operating systems. For FreeBSD,
they are provided in the form of a pkg mirror, so there is no need to
also have them in the FreeBSD Ports tree.
Approved by: bapt
Differential Revision: https://reviews.freebsd.org/D3643