Delete code corresponding to old UMA prefs.

components/metrics/metrics_pref_names.cc

Index: components/metrics/metrics_pref_names.cc
diff --git a/components/metrics/metrics_pref_names.cc b/components/metrics/metrics_pref_names.cc
index c6d12eda075bae3bf66dfb0da4741a4f54f26917..187b9042aded82c0dc110b51c3580319f152f554 100644
--- a/components/metrics/metrics_pref_names.cc
+++ b/components/metrics/metrics_pref_names.cc
@@ -32,14 +32,6 @@ const char kMetricsLowEntropySource[] =
 // stored locally and never transmitted in metrics reports.
 const char kMetricsMachineId[] = "user_experience_metrics.machine_id";
 
-// Old client id and low entropy source values, cleared the first time this
-// version is launched.
-// TODO(asvitkine): Delete these after a few releases have gone by and old
-// values have been cleaned up. http://crbug.com/357704
-const char kMetricsOldClientID[] = "user_experience_metrics.client_id";
-const char kMetricsOldLowEntropySource[] =
-    "user_experience_metrics.low_entropy_source";
-
 // Array of strings that are each UMA logs that were not sent because the
 // browser terminated before these accumulated metrics could be sent.  These
 // logs typically include histograms and memory reports, as well as ongoing