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>.
fzf is a general-purpose command-line fuzzy finder. It's an
interactive Unix filter for command-line that can be used with any
list; files, command history, processes, hostnames, bookmarks, git
commits, etc.