Use the new isNetworkSupported api for wifi-only

Didn't have an API for this before so people used a hacked system property (ro.carrier)
to determine if the device supported mobile data.  Added new API and switching callsites.

bug:5087537
Change-Id: Ibd799559be102a9e2fd552d1a23d1afbcf8f4614

src/com/android/settings/DateTimeSettings.java

@@ -94,7 +94,7 @@ public class DateTimeSettings extends SettingsPreferenceFragment
         mAutoTimeZonePref = (CheckBoxPreference) findPreference(KEY_AUTO_TIME_ZONE);
         // Override auto-timezone if it's a wifi-only device or if we're still in setup wizard.
         // TODO: Remove the wifiOnly test when auto-timezone is implemented based on wifi-location.
-        if (Utils.isWifiOnly() || isFirstRun) {
+        if (Utils.isWifiOnly(getActivity()) || isFirstRun) {
             getPreferenceScreen().removePreference(mAutoTimeZonePref);
             autoTimeZoneEnabled = false;
         }