Revert "[system-ota-tests] Switch to consuming packages.tar.gz"

This reverts commit c30d780d.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [system-ota-tests] Switch to consuming packages.tar.gz
> 
> Previously, infra tried to pass in the amber-files produced by
> the build into every test, but this was consuming too much
> space. Instead, this patch switches the system ota tests to
> consume the packages.tar.gz that's produced by the build.
> 
> Change-Id: I42e683d4b39f43544d755c8754649309c72de61b

TBR=ctiller@google.com,etryzelaar@google.com,computerdruid@google.com

Change-Id: I86e7c4675705fd99c7d1fe4f0936ebe3e81506e7
No-Presubmit: true
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