Stop using mVpns in getConnectionOwnerUid.

Use data that is already available in ConnectivityService
instead.

The behaviour of the new implementation is slightly different
from Q and R code when the permission check fails.

- The old code would throw a SecurityException if an app that
  was not an active VPN called the method, and would return
  INVALID_UID if the connection belonged to a UID that was not
  subject to the VPN.
- The new code returns INVALID_UID in both cases.

This does not seem like a compatibility problem. The only case in
which the code throws SecurityException is if the app is not a
current VPN app, but the app already knows whether it is or not.
The docs don't mention that the method SecurityException, either.

Bug: 173331190
Test: atest FrameworksNetTests
Test: atest HostsideVpnTests
Change-Id: If3d031e74df33b5c97e12ebf02272faac6769d50

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -8567,11 +8567,7 @@ public class ConnectivityServiceTest {
         final int myUid = Process.myUid();
         setupConnectionOwnerUidAsVpnApp(myUid, VpnManager.TYPE_VPN_PLATFORM);
 
-        try {
-            mService.getConnectionOwnerUid(getTestConnectionInfo());
-            fail("Expected SecurityException for non-VpnService app");
-        } catch (SecurityException expected) {
-        }
+        assertEquals(INVALID_UID, mService.getConnectionOwnerUid(getTestConnectionInfo()));
     }
 
     @Test
@@ -8579,11 +8575,7 @@ public class ConnectivityServiceTest {
         final int myUid = Process.myUid();
         setupConnectionOwnerUidAsVpnApp(myUid + 1, VpnManager.TYPE_VPN_SERVICE);
 
-        try {
-            mService.getConnectionOwnerUid(getTestConnectionInfo());
-            fail("Expected SecurityException for non-VpnService app");
-        } catch (SecurityException expected) {
-        }
+        assertEquals(INVALID_UID, mService.getConnectionOwnerUid(getTestConnectionInfo()));
     }
 
     @Test