lang/go/go-package.mk install several files that are not needed for packages
that just install a program. Define `do-install' target to avoid that.
While here also install fzf-tmux in bin/, man pages under ${PKGMANDIR}
accordingly and shell completions/bindings and vim plugin under
share/fzf. Update MESSAGE to reflect this change.
PKGREVISION++
Discussed with <maya>.