Remove default config alert

We don't exit here, so it's not a fatal error. It's also a fairly common
scenario, so remove the alert completely.

vncviewer/vncviewer.cxx

@@ -554,8 +554,6 @@ int main(int argc, char** argv)
     }
   } catch (rfb::Exception& e) {
     vlog.error("%s", e.str());
-    if (alertOnFatalError)
-      fl_alert("%s", e.str());
   }
 
   for (int i = 1; i < argc;) {