[signin] Remove deprecated pref kGoogleServicesUsername

This pref is deprecated since M43 and can now be removed.

TBR=jzw

Change-Id: Ie01b4946af6453f786aa05a348ce51c8e3477f39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787782
Commit-Queue: David Roger <[email protected]>
Reviewed-by: Monica Basta <[email protected]>
Cr-Commit-Position: refs/heads/master@{#695101}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 2bdbd99..45e09c1 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -495,6 +495,9 @@
 // Deprecated 8/2019
 const char kHintLoadedCounts[] = "optimization_guide.hint_loaded_counts";
 
+// Deprecated 9/2019
+const char kGoogleServicesUsername[] = "google.services.username";
+
 // Register prefs used only for migration (clearing or moving to a new key).
 void RegisterProfilePrefsForMigration(
     user_prefs::PrefRegistrySyncable* registry) {
@@ -571,6 +574,7 @@
   registry->RegisterBooleanPref(kInsecureExtensionUpdatesEnabled, false);
 
   registry->RegisterDictionaryPref(kHintLoadedCounts);
+  registry->RegisterStringPref(kGoogleServicesUsername, std::string());
 }
 
 }  // namespace
@@ -1179,4 +1183,7 @@
   // Added 8/2019
   profile_prefs->ClearPref(kInsecureExtensionUpdatesEnabled);
   profile_prefs->ClearPref(kHintLoadedCounts);
+
+  // Added 9/2019
+  profile_prefs->ClearPref(kGoogleServicesUsername);
 }