Removed all references to "Google Wi-Fi Assistant" from Settings.

+ Removed Wi-Fi Assistant message in Wi-Fi Advanced since it was
overridden by the Wi-Fi Assistant.
+ Removed Wi-Fi Assistant message in Wi-Fi Assistant Card.  Instead,
it is programatically created when the scorer is known.
+ "Google" was replaced with a placeholder.

Bug: 17457236
Change-Id: If3aab06c911ecf6ec13cbf00dea2fe9333abc1fc

res/xml/wifi_advanced_settings.xml

@@ -33,7 +33,6 @@
     <SwitchPreference
             android:key="wifi_assistant"
             android:title="@string/wifi_automatically_manage_title"
-            android:summary="@string/wifi_assistant_setting_summary"
             android:persistent="false" />
 
     <ListPreference