cgroups: Don't leave child processes behind anymore.

CL:59361 seems to have broken the cgroups functionality, so that
when you hit stop build, children stick around forever. Revert it
for now.

BUG=chromium:289760
TEST=Run locally and confirm that killing cbuildbot kills the other
     processes.

This reverts commit fd21f852e41281445bc9a2e8141e0a421d1b62c4.

Change-Id: Iba7ca556bf684bd1623d3768684add8cda1fe32d
Reviewed-on: https://chromium-review.googlesource.com/169000
Reviewed-by: Marc MERLIN <merlin@chromium.org>
Commit-Queue: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index b558217..f994910 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -544,21 +544,17 @@
   def RunStages(self):
     """Runs simple builder logic and publishes information to overlays."""
     was_build_successful = False
-    with cleanup.EnforcedCleanupSection() as critical_section:
-      try:
-        # Mark everything between EnforcedCleanupSection and here as having to
-        # be rolled back via the contextmanager cleanup handlers.
-        critical_section.ForkWatchdog()
-        super(DistributedBuilder, self).RunStages()
-        was_build_successful = results_lib.Results.BuildSucceededSoFar()
-      except SystemExit as ex:
-        # If a stage calls sys.exit(0), it's exiting with success, so that means
-        # we should mark ourselves as successful.
-        if ex.code == 0:
-          was_build_successful = True
-        raise
-      finally:
-        self.Publish(was_build_successful)
+    try:
+      super(DistributedBuilder, self).RunStages()
+      was_build_successful = results_lib.Results.BuildSucceededSoFar()
+    except SystemExit as ex:
+      # If a stage calls sys.exit(0), it's exiting with success, so that means
+      # we should mark ourselves as successful.
+      if ex.code == 0:
+        was_build_successful = True
+      raise
+    finally:
+      self.Publish(was_build_successful)
 
 
 def _ConfirmBuildRoot(buildroot):