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
diff --git a/service/proguard.flags b/service/proguard.flags
index cf25f05..ed9a65f 100644
--- a/service/proguard.flags
+++ b/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);
+}
diff --git a/thread/service/Android.bp b/thread/service/Android.bp
index 69295cc..0132235 100644
--- a/thread/service/Android.bp
+++ b/thread/service/Android.bp
@@ -47,9 +47,6 @@
         "ot-daemon-aidl-java",
     ],
     apex_available: ["com.android.tethering"],
-    optimize: {
-        proguard_flags_files: ["proguard.flags"],
-    },
 }
 
 cc_library_shared {
diff --git a/thread/service/proguard.flags b/thread/service/proguard.flags
deleted file mode 100644
index 5028982..0000000
--- a/thread/service/proguard.flags
+++ /dev/null
@@ -1,4 +0,0 @@
-# Ensure the callback methods are not stripped
--keepclassmembers class **.ThreadNetworkControllerService$ThreadNetworkCallback {
-    *;
-}