Deprecate Go library ports

Many of them are out of date now and there are few reasons to have
them in the tree [1].

[1] https://www.freebsd.org/doc/en/books/porters-handbook/go-libs.html

PR: 236502
Reviewed by: dg@syrec.org
Approved by: portmgr (mat), jlaffaye, wen, olgeni
Differential Revision: https://reviews.freebsd.org/D19568