Remove unused DRP code for migrating prefs

components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc b/components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc
index 52acb0cc4bf8003e0c0a55e160a609084c2bb6cf..cd72646424fda4f4e3536897d2ebbcd313148bd3 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.cc
@@ -233,10 +233,5 @@ const char kLoFiWasUsedThisSession[] =
 const char kSimulatedConfigRetrieveTime[] =
     "data_reduction.simulated_config_retrieve_time";
 
-// A boolean specifying whether the data reduction proxy statistics preferences
-// have migrated from local state to the profile.
-const char kStatisticsPrefsMigrated[] =
-    "data_reduction.statistics_prefs_migrated";
-
 }  // namespace prefs
 }  // namespace data_reduction_proxy