Delete code corresponding to old UMA prefs.

components/metrics/metrics_state_manager.cc

Index: components/metrics/metrics_state_manager.cc
diff --git a/components/metrics/metrics_state_manager.cc b/components/metrics/metrics_state_manager.cc
index 477751bd8894fe6fc418e5ee5fae82a00abc9784..db14f9fbb9054717971d1f451eceace3f3e13443 100644
--- a/components/metrics/metrics_state_manager.cc
+++ b/components/metrics/metrics_state_manager.cc
@@ -208,11 +208,6 @@ void MetricsStateManager::RegisterPrefs(PrefRegistrySimple* registry) {
 
   ClonedInstallDetector::RegisterPrefs(registry);
   CachingPermutedEntropyProvider::RegisterPrefs(registry);
-
-  // TODO(asvitkine): Remove these once a couple of releases have passed.
-  // http://crbug.com/357704
-  registry->RegisterStringPref(prefs::kMetricsOldClientID, std::string());
-  registry->RegisterIntegerPref(prefs::kMetricsOldLowEntropySource, 0);
 }
 
 void MetricsStateManager::BackUpCurrentClientInfo() {