Remove the enable flag from all plugins after the option has been ported.

chrome/browser/plugins/plugin_prefs.cc

Index: chrome/browser/plugins/plugin_prefs.cc
diff --git a/chrome/browser/plugins/plugin_prefs.cc b/chrome/browser/plugins/plugin_prefs.cc
index 0c418d1cdd0cbc649bcdff0d001ad39740ade5db..4dcae31beafe32a0c5e3b3f4003cfc8805306cfd 100644
--- a/chrome/browser/plugins/plugin_prefs.cc
+++ b/chrome/browser/plugins/plugin_prefs.cc
@@ -136,9 +136,9 @@ void PluginPrefs::SetPrefs(PrefService* prefs) {
           continue;  // Oops, don't know what to do with this item.
         }
 
-        bool enabled;
-        if (!plugin->GetBoolean("enabled", &enabled))
-          enabled = true;
+        bool enabled = true;
+        if (plugin->GetBoolean("enabled", &enabled))
+          plugin->Remove("enabled", nullptr);
 
         // Migrate disabled plugins and re-enable them all internally.
         // TODO(http://crbug.com/662006): Remove migration eventually.