Revert of Add field_specs to all metrics in luci-py

appengine/gce-backend/metrics.py

Index: appengine/gce-backend/metrics.py
diff --git a/appengine/gce-backend/metrics.py b/appengine/gce-backend/metrics.py
index aeafba5faac8df93986983d0b568514bb94652eb..e8cb950ce1239220f01228ac5525b6c85211bc92 100644
--- a/appengine/gce-backend/metrics.py
+++ b/appengine/gce-backend/metrics.py
@@ -26,16 +26,14 @@
 GLOBAL_METRICS = {
     'instances': gae_ts_mon.GaugeMetric(
         'machine_provider/gce_backend/instances',
-        'Current count of the number of instances.',
-        [gae_ts_mon.StringField('instance_template')]
+        description='Current count of the number of instances.',
     ),
 }
 
 
 config_valid = gae_ts_mon.BooleanMetric(
     'machine_provider/gce_backend/config/valid',
-    'Whether or not the current config is valid.',
-    [gae_ts_mon.StringField('config')],
+    description='Whether or not the current config is valid.',
 )