update_engine: Remove legacy logic and tests.

This removes logic that was used for tracking whether updates were
disabled by device policy, and unit tests that checked for the presence
of such logic. This logic is now part of the Update Manager's
UpdateCheckAllowed policy request. It is safe to remove the old check
because it'll always conclude that the update request can be sent, given
that the said policy has concluded the same.

BUG=None
TEST=Unit tests.

Change-Id: Ibbb3728f7239f608a6317bc5a8b76cac7f54bc5f
Reviewed-on: https://chromium-review.googlesource.com/220876
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
diff --git a/update_attempter.cc b/update_attempter.cc
index bc18945..9a91d51 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -409,9 +409,7 @@
     omaha_request_params_->UpdateDownloadChannel();
   }
 
-  LOG(INFO) << "update_disabled = "
-            << utils::ToString(omaha_request_params_->update_disabled())
-            << ", target_version_prefix = "
+  LOG(INFO) << "target_version_prefix = "
             << omaha_request_params_->target_version_prefix()
             << ", scatter_factor_in_seconds = "
             << utils::FormatSecs(scatter_factor_.InSeconds());