Fix leaking IntentReceiver in SettingsActivity

We added a new IntentReceiver to notice users being added and
removed, but missed unregistering it where appropriate.

Change-Id: I3ca1d7c8916870066dda34b830e100948dd4481c
diff --git a/src/com/android/settings/SettingsActivity.java b/src/com/android/settings/SettingsActivity.java
index 3014225..de66aea 100644
--- a/src/com/android/settings/SettingsActivity.java
+++ b/src/com/android/settings/SettingsActivity.java
@@ -778,6 +778,7 @@
     protected void onPause() {
         super.onPause();
         unregisterReceiver(mBatteryInfoReceiver);
+        unregisterReceiver(mUserAddRemoveReceiver);
         mDynamicIndexableContentMonitor.unregister();
     }