Partially Revert 2b9d2417

2b9d2417 update_engine: Update libchrome APIS to r456626.

The above commit changes the libchrome API used in update_engine to r456626. But
the libchrome has not been upreved fully in the CrOS yet with the exception of
some changes represented in UE like CL:882543. So, now we need to revert the
changes partially untill the libchrome is updated.

BUG=chromium:815356
TEST=unittests, precq

Change-Id: If2207f0672c7b9f6dab84e676d9fb8423a047372
Reviewed-on: https://chromium-review.googlesource.com/965266


Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>