autotest: delete some email alerts; replace some with monarch metrics

For email alerts that seem (based on searching my email) to never be
sent, I simply deleted them.

For those that are sent sometimes and seem easily amenable to a monarch
metric instead, I changed them to a metric.

This is a first step; there are still many remaining unneccesary email
alerts.

BUG=chromium:672726
TEST=None

Change-Id: Ib1d3715e618623faa16f3faaceabf4218dbad49a
Reviewed-on: https://chromium-review.googlesource.com/420468
Commit-Ready: Aviv Keshet <akeshet@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/scheduler/monitor_db_cleanup.py b/scheduler/monitor_db_cleanup.py
index 51d3567..fd5d73b 100644
--- a/scheduler/monitor_db_cleanup.py
+++ b/scheduler/monitor_db_cleanup.py
@@ -147,13 +147,10 @@
                 first_model, first_field, second_model, second_field))
 
         if errors:
-            subject = ('%s relationships to invalid models, cleaned all' %
-                       len(errors))
-            message = '\n'.join(errors)
-            logging.warning(subject)
-            logging.warning(message)
-            email_manager.manager.enqueue_notify_email(subject, message)
-
+            m = 'chromeos/autotest/scheduler/cleanup/invalid_models_cleaned'
+            metrics.Counter(m).increment_by(len(errors))
+            logging.warn('Cleaned invalid models due to errors: %s'
+                         % ('\n'.join(errors)))
 
     def _clear_inactive_blocks(self):
         msg = 'Clear out blocks for all completed jobs.'