Remove reference when active listener is unregistered

The registered listeners are added into internal ArrayMap as a
reference but are not removed when the listeners are
unregistered. The actions for registration should be done in
pairs.

Test: atest FrameworksNetTests
Change-Id: Id9e674f5104d1471dd81224b6a271a8a92172e34

tests/unit/java/android/net/ConnectivityManagerTest.java

@@ -326,6 +326,8 @@ public class ConnectivityManagerTest {
         verify(mService, times(1)).registerNetworkActivityListener(any());
         manager.removeDefaultNetworkActiveListener(listener);
         verify(mService, times(1)).unregisterNetworkActivityListener(any());
+        assertThrows(IllegalArgumentException.class,
+                () -> manager.removeDefaultNetworkActiveListener(listener));
     }
 
     @Test