Simplify bash_completions.go

Improve test coverage from 80% to 85%.

bash_completions_test.go

@@ -2,16 +2,12 @@ package cobra
 
 import (
 	"bytes"
-	"fmt"
 	"os"
 	"os/exec"
 	"strings"
 	"testing"
 )
 
-var _ = fmt.Println
-var _ = os.Stderr
-
 func checkOmit(t *testing.T, found, unexpected string) {
 	if strings.Contains(found, unexpected) {
 		t.Errorf("Unexpected response.\nGot: %q\nBut should not have!\n", unexpected)