Merge pull request #34906 from luxas/remove_old_networking

Automatic merge from submit-queue

WIP: Remove the legacy networking mode

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**What this PR does / why we need it**:
Removes the deprecated configure-cbr0 flag and networking mode to avoid having untested and maybe unstable code in kubelet, see: #33789

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, #<issue_number>, ...)` format, will close that issue when PR gets merged)*: 
fixes #30589
fixes #31937

**Special notes for your reviewer**: There are a lot of deployments who rely on this networking mode. Not sure how we deal with that: force switch to kubenet or just delete the old deployment?

But please review the code changes first (the first commit)

**Release note**:
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```release-note
Removed the deprecated kubelet --configure-cbr0 flag, and with that the "classic" networking mode as well
```

PTAL @kubernetes/sig-network @kubernetes/sig-node @mikedanese

cluster/common.sh

@@ -772,7 +772,6 @@ KUBERNETES_CONTAINER_RUNTIME: $(yaml-quote ${CONTAINER_RUNTIME:-rkt})
 RKT_VERSION: $(yaml-quote ${RKT_VERSION:-})
 RKT_PATH: $(yaml-quote ${RKT_PATH:-})
 RKT_STAGE1_IMAGE: $(yaml-quote ${RKT_STAGE1_IMAGE:-})
-KUBERNETES_CONFIGURE_CBR0: $(yaml-quote ${KUBERNETES_CONFIGURE_CBR0:-true})
 EOF
   fi
   if [[ "${ENABLE_CLUSTER_AUTOSCALER}" == "true" ]]; then