Move hyperkube symlink creation to base image and re-enable building of conformance image

[ixdy]

What this PR does / why we need it: currently when building the conformance and hyperkube images, we call docker run --rm --privileged multiarch/qemu-user-static:register --reset to register the qemu handlers, as we run non-x86 binaries inside the Dockerfiles.

This really isn't that necessary, however:

• for hyperkube, we're just creating some symlinks
• for conformance, we aren't even running any commands. It's just a result of copy-pasting the Dockerfile from hyperkube.

I've moved the symlink creation to the hyperkube base image, which prevents us from needing to run this at build time, and thus from needing to run the privileged container at all.

The only negative side effect of this is that the conformance image has some dangling symlinks to the nonexistent hyperkube binary. But it probably shouldn't be using the hyperkube image, anyway...

I've also updated the hyperkube symlinks, adding the missing cloud-controller-manager symlink and removing the deprecated aggregator symlink.

This probably doesn't break anything, but with hyperkube, you never really know.

I haven't promoted the new hyperkube base image yet, so this will fail builds. If we think this approach looks reasonable, I'll work on promoting the image.

Release note:

NONE

/assign @cblecker @dims @BenTheElder @mkumatag @AishSundar

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[ixdy]

this also re-enables building the conformance image.

[AishSundar]

@timothysc and @dougm as FYI

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[ixdy]

/retest

[dims]

/kind cleanup
/lgtm
/hold

(please remove hold when you think this is ready)

[ixdy]

/hold cancel
PTAL

[BenTheElder]

/lgtm

[ixdy]

flake, I think?
/retest

[dims]

/test pull-kubernetes-node-e2e