Stop enabling afterburn-hostname.service on GCP

[jlebon]

Right now, RHCOS is carrying a patch for Afterburn to have it write to /etc/hostname (basically coreos/afterburn#512).

There's a lot of backstory on this also in coreos/afterburn#509. But IIUC, now that NM correctly shortens DHCP hostnames that are too long, we can rely on hostname setting via DHCP again and stop carrying that patch.

A big change here of course is that we'd no longer physically write /etc/hostname from the initramfs. Need to verify this doesn't break things. (Though presumably this works in OKD + FCOS today, where we don't have that patch.)

[openshift-bot]

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/lifecycle stale

[jlebon]

/remove-lifecycle stale

[openshift-bot]

Issues go stale after 90d of inactivity.

Mark the issue as fresh by commenting /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.
Exclude this issue from closing by commenting /lifecycle frozen.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[jlebon]

/remove-lifecycle stale