Remove --use-real-proxier support from kubemark

[danwinship]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

kubemark's proxy mode exists to test how kube-proxy affects the load on the apiserver, not how it affects the load on the node. There's no need to generate fake iptables commands, because that all happens entirely independently of the api watchers.

It looks like sig-scalability's jobs turn this flag off anyway, as does the suggested template so this is just getting rid of something probably no one was using (and making kubemark slightly less dependent on undocumented internals of kube-proxy).

(I see there are comments in the kubemark source about splitting up the hollow kubelet and hollow proxy more... We could just add --proxy-mode=hollow to the kube-proxy binary if you wanted...)

Which issue(s) this PR fixes:

none

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

I think? kubemark is just for k8s devs, not end users, right?

/assign @wojtek-t
/sig scalability

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[wojtek-t]

/lgtm
/approve

Thanks!

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: b50ee0f3805978b5018291096f7202e24f4521f6

[wojtek-t]

/lgtm

/assign @liggitt - for vendor change

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 220fe65d078a32b40597da15a0b6e5e7ee185bd0

[liggitt]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: danwinship, liggitt, wojtek-t

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Needs approval from an approver in each of these files:

• cmd/kubemark/OWNERS [liggitt,wojtek-t]
• pkg/proxy/kubemark/OWNERS [danwinship,liggitt,wojtek-t]
• vendor/OWNERS [liggitt]

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