[dPWA] Remove old ExternallyInstalledWebAppPrefs code

This CL removes ExternallyInstalledWebAppPrefs and all associated
migration code. Metrics show the migration has applied to the vast
majority of users: go/ytyjd

Fixed: 1339965
Change-Id: Iddb710e5b301798b9964cc3b81a8210906d4344e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4587571
Commit-Queue: Alan Cutter <[email protected]>
Reviewed-by: Dibyajyoti Pal <[email protected]>
Reviewed-by: Tim Sergeant <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1154214}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index cdd7f49..446ce725 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -874,6 +874,9 @@
     "SupervisedUserHasIncompleteKey";
 #endif
 
+// Deprecated 06/2023.
+const char kWebAppsExtensionIDs[] = "web_apps.extension_ids";
+
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
@@ -1237,6 +1240,9 @@
 #if BUILDFLAG(IS_CHROMEOS_ASH)
   registry->RegisterBooleanPref(kEventRemappedToRightClick, false);
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
+
+  // Deprecated 06/2023.
+  registry->RegisterDictionaryPref(kWebAppsExtensionIDs);
 }
 
 }  // namespace
@@ -2335,6 +2341,9 @@
   profile_prefs->ClearPref(kSamlPasswordSyncToken);
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 
+  // Added 06/2023.
+  profile_prefs->ClearPref(kWebAppsExtensionIDs);
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_PROFILE_PREFS