Make the fragment title can’t searchable

we shouldn't take users so deep into the settings IA because it's easy
to feel lost in settings after clicking on a result without additional
context.

Bug: 143055215
Test: robotest & manual
Change-Id: I337cb5ead31e1e4e7bf9be78132e90630f83ee43

res/xml/system_dashboard_fragment.xml

@@ -17,7 +17,6 @@
 <PreferenceScreen
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:settings="http://schemas.android.com/apk/res-auto"
-    android:key="system_dashboard_screen"
     android:title="@string/header_category_system"
     settings:initialExpandedChildrenCount="4">
 
@@ -76,4 +75,4 @@
                 android:targetClass="@string/additional_system_update_menu"/>
     </Preference>
 
-</PreferenceScreen>
+</PreferenceScreen>