builder/amazon/common: remove nil check on slice, len() on nil slices is zero

builder/amazon/common/ami_config_test.go

@@ -69,7 +69,6 @@ func TestAMIConfigPrepare_regions(t *testing.T) {
 	if errs = c.prepareRegions(accessConf); len(errs) > 0 {
 		t.Fatalf("shouldn't have err: %#v", errs)
 	}
-	errs = errs[:0]
 
 	c.AMIRegions = []string{"us-east-1", "us-west-1", "us-east-1"}
 	if errs = c.prepareRegions(accessConf); len(errs) > 0 {

builder/amazon/common/errors.go

@@ -24,7 +24,7 @@ type stsDecoder interface {
 func decodeAWSError(decoder stsDecoder, err error) error {
 
 	groups := encodedFailureMessagePattern.FindStringSubmatch(err.Error())
-	if groups != nil && len(groups) > 1 {
+	if len(groups) > 1 {
 		result, decodeErr := decoder.DecodeAuthorizationMessage(&sts.DecodeAuthorizationMessageInput{
 			EncodedMessage: aws.String(groups[2]),
 		})