Use the model hook and setupController hook instead of afterModel

This is a more idiomatic way to handle the QP resetting in the
application controller.

ui/app/routes/application.js

@@ -46,14 +46,15 @@ export default Route.extend({
     );
   },
 
-  // setupController doesn't refire when the model hook refires as part of
-  // a query param change
-  afterModel(model, transition) {
-    const queryParam = transition.queryParams.region;
-    const controller = this.controllerFor('application');
+  // Model is being used as a way to transfer the provided region
+  // query param to update the controller state.
+  model(params) {
+    return params.region;
+  },
+
+  setupController(controller, model) {
+    const queryParam = model;
 
-    // The default region shouldn't show up as a query param since
-    // it's superfluous.
     if (queryParam === this.get('system.defaultRegion.region')) {
       next(() => {
         controller.set('region', null);

ui/tests/acceptance/regions-test.js

@@ -137,7 +137,7 @@ test('switching regions to the default region, unsets the region query param', f
   selectChoose('[data-test-region-switcher]', defaultRegion);
 
   andThen(() => {
-    assert.equal(currentURL(), '/jobs', 'No region query param for the default region');
+    assert.notOk(currentURL().includes('region='), 'No region query param for the default region');
     assert.equal(
       window.localStorage.nomadActiveRegion,
       defaultRegion,