[paver] Revert: Switch install-disk-image to talk to paver service

This reverts commit ffcb46fb.

Reason for revert: This change broke OTA.

Original change's description:
> [paver] Switch install-disk-image to talk to paver service
> 
> The last change will be to have the netsvc talk to the paver service in
> order to pave, rather than have it call into the install-disk-image
> binary.
> 
> ZX-3861
> 
> Tested: Paved NUC, pixelbook, vim2, astro
> 
> Change-Id: If1e0651fbae9c13ea75cf8d1aea1c7fac3b130ee

TBR=smklein@google.com,abarth@google.com,surajmalhotra@google.com

Change-Id: Idd58a94448947373c29ae051d0f13ab8cbd87a05
No-Presubmit: true
No-Tree-Checks: true
No-Try: true