Move the Thread proguard flags to ConnectivityService's proguard.flags

We needed this proguard flag because
ThreadNetworkService#onLocalNetworkInfoChanged will otherwise be
stripped. We need to keep the method to ensure the border routing
feature works.

Initially we put the flag in thread/service/proguard.flags. However,
this seems not working on udc-mainline-prod branch. After moving it to
Connectivity/service/proguard.flags, it works as desired.

Bug: 313539492

Change-Id: I33cb0602095a617dbb1cfe3d9002f9c68e93cccf

service/proguard.flags

@@ -15,3 +15,7 @@
     static final % EVENT_*;
 }
 
+# b/313539492 Keep the onLocalNetworkInfoChanged method in classes extending Connectivity.NetworkCallback.
+-keepclassmembers class * extends **android.net.ConnectivityManager$NetworkCallback {
+    public void onLocalNetworkInfoChanged(**android.net.Network, **android.net.LocalNetworkInfo);
+}

thread/service/Android.bp

@@ -47,9 +47,6 @@ java_library {
         "ot-daemon-aidl-java",
     ],
     apex_available: ["com.android.tethering"],
-    optimize: {
-        proguard_flags_files: ["proguard.flags"],
-    },
 }
 
 cc_library_shared {

thread/service/proguard.flags

-# Ensure the callback methods are not stripped
--keepclassmembers class **.ThreadNetworkControllerService$ThreadNetworkCallback {
-    *;
-}