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/storage/redis/redis-proxy.yaml

@@ -1,14 +0,0 @@
-apiVersion: v1
-kind: Pod
-metadata:
-  labels:
-    name: redis-proxy
-    role: proxy
-  name: redis-proxy
-spec:
-  containers:
-  - name: proxy
-    image: kubernetes/redis-proxy:v2
-    ports:
-    - containerPort: 6379
-      name: api