daemon/logger/splunk: remove uses of pkg/urlutil.IsURL()

pkg/urlutil (despite its poorly chosen name) is not really intended as a generic
utility to handle URLs, and should only be used by the builder to handle (remote)
build contexts.

This patch removes the use of urlutil.IsURL(), in favor of just checking if the
provided scheme (protocol) is supported.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/logger/splunk/splunk.go

@@ -22,7 +22,6 @@ import (
 	"github.com/docker/docker/daemon/logger"
 	"github.com/docker/docker/daemon/logger/loggerutils"
 	"github.com/docker/docker/pkg/pools"
-	"github.com/docker/docker/pkg/urlutil"
 	"github.com/google/uuid"
 	"github.com/sirupsen/logrus"
 )
@@ -607,8 +606,8 @@ func parseURL(info logger.Info) (*url.URL, error) {
 		return nil, fmt.Errorf("%s: failed to parse %s as url value in %s", driverName, splunkURLStr, splunkURLKey)
 	}
 
-	if !urlutil.IsURL(splunkURLStr) ||
-		!splunkURL.IsAbs() ||
+	if !splunkURL.IsAbs() ||
+		(splunkURL.Scheme != "http" && splunkURL.Scheme != "https") ||
 		(splunkURL.Path != "" && splunkURL.Path != "/") ||
 		splunkURL.RawQuery != "" ||
 		splunkURL.Fragment != "" {