just use setup (#1574)

All these functions are namespaced by their package anyway; just use
setup().

plugin/bind/bind.go

@@ -6,6 +6,6 @@ import "github.com/mholt/caddy"
 func init() {
 	caddy.RegisterPlugin("bind", caddy.Plugin{
 		ServerType: "dns",
-		Action:     setupBind,
+		Action:     setup,
 	})
 }