http: remove dualstack since its deprecated (#16940)

Deprecated: Fast Fallback is enabled by default. To
disable, set FallbackDelay to a negative value.

https://golang.org/src/net/dial.go

pkg/cmd/grafana-cli/services/services.go

@@ -32,7 +32,6 @@ func Init(version string, skipTLSVerify bool) {
 		DialContext: (&net.Dialer{
 			Timeout:   30 * time.Second,
 			KeepAlive: 30 * time.Second,
-			DualStack: true,
 		}).DialContext,
 		MaxIdleConns:          100,
 		IdleConnTimeout:       90 * time.Second,