TetherUtil: Use ConnectivityManager for tethering

In the past, enabling the SoftAP would cause tethering to happen because
of some unfortunate side effects.  This is no longer the case, and
using WifiManager for this purpose is not a good idea.

Bug: 30147602
Test: Can toggle tethering on/off via all of settings, quick settings,
      and quick quick settings.

Change-Id: Iebbfc6c48b3e8e3fa52d235594ded3502f5801a3
(cherry picked from commit 26bd4efcaaad4a866310d6421909645e81167d1f)
diff --git a/packages/SettingsLib/src/com/android/settingslib/TetherUtil.java b/packages/SettingsLib/src/com/android/settingslib/TetherUtil.java
index d368de9..151e0ea 100644
--- a/packages/SettingsLib/src/com/android/settingslib/TetherUtil.java
+++ b/packages/SettingsLib/src/com/android/settingslib/TetherUtil.java
@@ -16,18 +16,11 @@
 package com.android.settingslib;
 
 import android.content.Context;
-import android.net.wifi.WifiManager;
 import android.os.SystemProperties;
 import android.telephony.CarrierConfigManager;
 
 public class TetherUtil {
 
-    public static boolean setWifiTethering(boolean enable, Context context) {
-        final WifiManager wifiManager =
-                (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
-        return wifiManager.setWifiApEnabled(null, enable);
-    }
-
     private static boolean isEntitlementCheckRequired(Context context) {
         final CarrierConfigManager configManager = (CarrierConfigManager) context
              .getSystemService(Context.CARRIER_CONFIG_SERVICE);