Outbound: One endpoint and at most one user only (#5144)

https://github.com/XTLS/Xray-core/pull/5124#issuecomment-3281091009

Fixes https://github.com/XTLS/Xray-core/pull/5124#pullrequestreview-3218097421

core/xray_test.go

@@ -63,17 +63,13 @@ func TestXrayClose(t *testing.T) {
 		Outbound: []*OutboundHandlerConfig{
 			{
 				ProxySettings: serial.ToTypedMessage(&outbound.Config{
-					Receiver: []*protocol.ServerEndpoint{
-						{
-							Address: net.NewIPOrDomain(net.LocalHostIP),
-							Port:    uint32(0),
-							User: []*protocol.User{
-								{
-									Account: serial.ToTypedMessage(&vmess.Account{
-										Id: userID.String(),
-									}),
-								},
-							},
+					Receiver: &protocol.ServerEndpoint{
+						Address: net.NewIPOrDomain(net.LocalHostIP),
+						Port:    uint32(0),
+						User:  &protocol.User{
+							Account: serial.ToTypedMessage(&vmess.Account{
+								Id: userID.String(),
+							}),
 						},
 					},
 				}),