Deprecate multiple endpoints for out-of-cluster k8s api (#2454)

This fix deprecates endpoints for out-of-cluster k8s api,
The Corefile still takes multiple endpoints though only
the first one is used. A warning is shown if there are
multiple endpoints.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/kubernetes/setup_test.go

@@ -394,19 +394,6 @@ kubernetes cluster.local`,
 			podModeDisabled,
 			fall.Zero,
 		},
-		{
-			`kubernetes coredns.local {
-    endpoint http://localhost:9090 https://localhost:9091
-}`,
-			true,
-			"multiple endpoints can only accept http",
-			-1,
-			-1,
-			defaultResyncPeriod,
-			"",
-			podModeDisabled,
-			fall.Zero,
-		},
 	}
 
 	for i, test := range tests {