fix example

example/example.go

@@ -1,14 +0,0 @@
-package main
-
-import "github.com/alexflint/go-arg"
-
-func main() {
-	var args struct {
-		Input    string   `arg:"positional"`
-		Output   []string `arg:"positional"`
-		Verbose  bool     `arg:"-v,help:verbosity level"`
-		Dataset  string   `arg:"help:dataset to use"`
-		Optimize int      `arg:"-O,help:optimization level"`
-	}
-	arg.MustParse(&args)
-}