fix: linter issue

megacheck, gosimple and unused has been deprecated and subsumed by
staticcheck. And staticcheck also has been upgraded. we need to update
code for the linter issue.

close: #2945

Signed-off-by: Wei Fu <fuweid89@gmail.com>

archive/tar_test.go

@@ -329,7 +329,7 @@ func TestBreakouts(t *testing.T) {
 			if err != nil {
 				return err
 			}
-			if bytes.Compare(b, content) != 0 {
+			if !bytes.Equal(b, content) {
 				return errors.Errorf("content differs: expected %v, got %v", content, b)
 			}
 			return nil
@@ -1179,7 +1179,7 @@ func fileEntry(name string, expected []byte, mode int) tarEntryValidator {
 		if hdr.Mode != int64(mode) {
 			return errors.Errorf("wrong mode %o, expected %o", hdr.Mode, mode)
 		}
-		if bytes.Compare(b, expected) != 0 {
+		if !bytes.Equal(b, expected) {
 			return errors.Errorf("different file content")
 		}
 		return nil

archive/tar_windows.go

@@ -74,7 +74,7 @@ func tarName(p string) (string, error) {
 	// in file names, it is mostly safe to replace however we must
 	// check just in case
 	if strings.Contains(p, "/") {
-		return "", fmt.Errorf("Windows path contains forward slash: %s", p)
+		return "", fmt.Errorf("windows path contains forward slash: %s", p)
 	}
 
 	return strings.Replace(p, string(os.PathSeparator), "/", -1), nil
@@ -130,11 +130,7 @@ func skipFile(hdr *tar.Header) bool {
 	// specific or Linux-specific, this warning should be changed to an error
 	// to cater for the situation where someone does manage to upload a Linux
 	// image but have it tagged as Windows inadvertently.
-	if strings.Contains(hdr.Name, ":") {
-		return true
-	}
-
-	return false
+	return strings.Contains(hdr.Name, ":")
 }
 
 // handleTarTypeBlockCharFifo is an OS-specific helper function used by