Messaging: Remove compatibility for old android versions

Change-Id: Id9065d60525a509271a0e64c0e349e857cb998e2

src/com/android/messaging/BugleApplication.java

@@ -42,7 +42,6 @@ import com.android.messaging.util.BuglePrefs;
 import com.android.messaging.util.BuglePrefsKeys;
 import com.android.messaging.util.DebugUtils;
 import com.android.messaging.util.LogUtil;
-import com.android.messaging.util.OsUtil;
 import com.android.messaging.util.PhoneUtils;
 import com.android.messaging.util.Trace;
 
@@ -99,9 +98,7 @@ public class BugleApplication extends Application implements UncaughtExceptionHa
         // Fixup messages in flight if we crashed and send any pending
         dataModel.onApplicationCreated();
         // Register carrier config change receiver
-        if (OsUtil.isAtLeastM()) {
-            registerCarrierConfigChangeReceiver(context);
-        }
+        registerCarrierConfigChangeReceiver(context);
 
         Trace.endSection();
     }