Remove UNIQUENAME and LATEST_LINK.
UNIQUENAME was never unique, it was only used by USE_LDCONFIG and now,
we won't have conflicts there.
Use PKGBASE instead of LATEST_LINK in PKGLATESTFILE, the *only* consumer
is pkg-devel, and it works just fine without LATEST_LINK as pkg-devel
has the correct PKGNAME anyway.
Now that UNIQUENAME is gone, OPTIONSFILE is too. (it's been called
Reviewed by: antoine, bapt
Exp-run by: antoine
Sponsored by: Absolight
Differential Revision: https://reviews.freebsd.org/D3336