Go: fix test and remove unused code (#15909)

### What problem does this PR solve?

1. Fix go test, some cases still failed.
2. Remove unused code.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/cli/common_command.go

@@ -139,7 +139,7 @@ func (c *CLI) PingServer(iterations int) (ResponseIf, error) {
 	switch c.Config.CLIMode {
 	case AdminMode:
 		if err = json.Unmarshal(resp.Body, &result); err != nil {
-			return nil, fmt.Errorf("list users failed: invalid JSON (%w)", err)
+			return nil, fmt.Errorf("ping failed: invalid JSON (%w)", err)
 		}
 	case APIMode:
 		if string(resp.Body) == "pong" {