Cleanup the public API getActiveNetworkForUid on AOSP

In order to make ConnectivityService the mainline module in ANDROID 12,
The earliest ConnectivityService API getActiveNetworkForUid was exposed.

But after that public api getActiveNetworkForUid and all callers
(Outside the module) has been deleted or replaced in android 12
version. So we should delete the public API in AOSP to keep the APIs
of Android 12 & AOSP consistent and also avoid using it again in AOSP.
The commit is equivalent to ag/14029494, but done in a different repo.

Bug: 183465229
Test: atest ConnectivityControllerTest
Merged-In: I3c2563d4ae4e3715d0c6270344ba8f7ef067872f
Change-Id: I50a39d6391c88bbb914a63fdb17bae6851591c01

framework/src/android/net/ConnectivityManager.java

@@ -1187,7 +1187,8 @@ public class ConnectivityManager {
      *
      * @return a {@link Network} object for the current default network for the
      *         given UID or {@code null} if no default network is currently active
-     * TODO: b/183465229 Cleanup getActiveNetworkForUid once b/165835257 is fixed
+     *
+     * @hide
      */
     @RequiresPermission(android.Manifest.permission.NETWORK_STACK)
     @Nullable