Remove redis-proxy example

The docker image is nowhere to be found, so lets remove it.
There have been a request for the Dockerfile here [1], but nobody
seems to care.

redis-proxy is replaced with redis-master in test-cmd-util.sh, to
ensure that the tests still works.
The redis-proxy pod in test/fixtures/doc-yaml/user-guide/multi-pod.yaml
is replaced with valid-pod from test/fixtures/doc-yaml/admin/limitrange/valid-pod.yaml,
so redis-proxy is removed every where.

[1] https://github.com/kubernetes/kubernetes/issues/4914#issuecomment-77209779

examples/examples_test.go

@@ -284,7 +284,6 @@ func TestExampleObjectSchemas(t *testing.T) {
 		"../examples/storage/redis": {
 			"redis-controller":          &api.ReplicationController{},
 			"redis-master":              &api.Pod{},
-			"redis-proxy":               &api.Pod{},
 			"redis-sentinel-controller": &api.ReplicationController{},
 			"redis-sentinel-service":    &api.Service{},
 		},