Mk/Uses/go.mk: Drop PLIST_SUB for GO_PKGNAME

[tobik]

Summary

It is often too general and can produce bad results with make makeplist. For example, in mail/aerc it produces bogus entries like

man/man5/%%GO_PKGNAME%%-sendmail.5.gz

since GO_PKGNAME=aerc there. AFAICT this was only ever really useful for Go libraries, so I think we should drop it now.

Only 2 ports appear to use it currently which are easily fixed.

Test Plan

I have done no real testing so far. This might affect more ports. I will start some Poudriere test builds after we agree that this is the right thing to do.

[dmgk]

I'm traveling right now and cannot test this but it LGTM, thanks.

[tobik]

Thanks.

Tests builds were fine.