Use the util for deleting the custom lsb release.

BUG=chromium:1081031
TEST=OOBE and nonblockingoOBE

Change-Id: Iac69373dd2ef41b023cd00b595f4081ffa5b177a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2223718
Commit-Queue: David Haddock <dhaddock@chromium.org>
Tested-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/server/site_tests/autoupdate_ForcedOOBEUpdate/autoupdate_ForcedOOBEUpdate.py b/server/site_tests/autoupdate_ForcedOOBEUpdate/autoupdate_ForcedOOBEUpdate.py
index 05ebc2f..ab8f591 100644
--- a/server/site_tests/autoupdate_ForcedOOBEUpdate/autoupdate_ForcedOOBEUpdate.py
+++ b/server/site_tests/autoupdate_ForcedOOBEUpdate/autoupdate_ForcedOOBEUpdate.py
@@ -19,10 +19,11 @@
 
 
     def cleanup(self):
-        self._host.run('rm %s' % self._CUSTOM_LSB_RELEASE, ignore_status=True)
-
         # Get the last two update_engine logs: before and after reboot.
         self._save_extra_update_engine_logs(number_of_logs=2)
+
+        self._clear_custom_lsb_release()
+
         self._change_cellular_setting_in_update_engine(False)
 
         # Cancel any update still in progress.
diff --git a/server/site_tests/autoupdate_NonBlockingOOBEUpdate/autoupdate_NonBlockingOOBEUpdate.py b/server/site_tests/autoupdate_NonBlockingOOBEUpdate/autoupdate_NonBlockingOOBEUpdate.py
index b309e69..4df0b3a 100644
--- a/server/site_tests/autoupdate_NonBlockingOOBEUpdate/autoupdate_NonBlockingOOBEUpdate.py
+++ b/server/site_tests/autoupdate_NonBlockingOOBEUpdate/autoupdate_NonBlockingOOBEUpdate.py
@@ -15,7 +15,7 @@
 
     def cleanup(self):
         """Remove the custom lsb-release used by the test."""
-        self._host.run('rm %s' % self._CUSTOM_LSB_RELEASE, ignore_status=True)
+        self._clear_custom_lsb_release()
         super(autoupdate_NonBlockingOOBEUpdate, self).cleanup()