[autotest] Migrate graphite directory to client/common_lib/cros

This change allows us to report stats in client tests.
1. Change import paths for all files that import modules from graphite
2. Clean up some unused modules
Related CL: https://chromium-review.googlesource.com/#/c/202467/
BUG=chromium:237255
TEST=Ran scheduler locally, scheduled reboot jobs, verified stats such as monitor_db_cleanup.user_cleanup._cleanup were reported on chromeos-stats.
DEPLOY = apache, scheduler, host_scheduler
Change-Id: Iebfe3b8acc1c363a0b70ea555744e85d1367cb67
Reviewed-on: https://chromium-review.googlesource.com/202727
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Michael Liang <michaelliang@chromium.org>
Tested-by: Michael Liang <michaelliang@chromium.org>
diff --git a/frontend/afe/json_rpc/serviceHandler.py b/frontend/afe/json_rpc/serviceHandler.py
index dbf9181..ede705c 100644
--- a/frontend/afe/json_rpc/serviceHandler.py
+++ b/frontend/afe/json_rpc/serviceHandler.py
@@ -22,7 +22,7 @@
 import traceback
 
 from json import decoder, encoder
-from autotest_lib.site_utils.graphite import stats
+from autotest_lib.client.common_lib.cros.graphite import stats
 
 def customConvertJson(value):
     """\