Clean up old WinVNC services

We've changed the service name a couple of times for various
reasons. Make sure the old versions are removed when the new one
is registered.
diff --git a/win/winvnc/winvnc.cxx b/win/winvnc/winvnc.cxx
index ff16aac..57f9f3d 100644
--- a/win/winvnc/winvnc.cxx
+++ b/win/winvnc/winvnc.cxx
@@ -168,6 +168,11 @@
         runServer = false;
         int j = i;
         i = argc;
+
+        // Try to clean up earlier services we've had
+        rfb::win32::unregisterService("WinVNC4");
+        rfb::win32::unregisterService("TigerVNC Server");
+
         if (rfb::win32::registerService(VNCServerService::Name,
                                         _T("TigerVNC Server"),
                                         _T("Provides remote access to this machine via the VNC/RFB protocol."),