Remove test that exits if no userDir defined

With the storage plugins it is possible to not need a userDir, just a
settings.js

packages/node_modules/node-red/red.js

@@ -321,11 +321,6 @@ httpsPromise.then(function(startupHttps) {
         settings.userDir = parsedArgs.userDir;
     }
 
-    if (!settings.userDir) {
-        console.log("No Node-RED userDir set, exiting")
-        process.exit(1)
-    }
-
     try {
         RED.init(server,settings);
     } catch(err) {