Deprecate devel/go-gocode

devel/go-gocode has issues working with Go versions 1.10 and later [1].

[1] https://github.com/nsf/gocode/blob/master/README.md

PR: 235352
Submitted by: Dmitri Goutnik <dg@syrec.org>
Approved by: cs (maintainer timeout, 2 months)