Simplify our capabilities stub assignment

This is more legible but still gets the point across; the intermediate
variable was explicit but ultimately unnnecessary.

x-pack/plugins/ml/server/shared_services/providers/modules.ts

@@ -43,8 +43,7 @@ export function getModulesProvider({
     ) {
       let hasMlCapabilities: HasMlCapabilities;
       if (request.params === 'DummyKibanaRequest') {
-        const hasMlCapabilitiesStub = () => Promise.resolve();
-        hasMlCapabilities = hasMlCapabilitiesStub;
+        hasMlCapabilities = () => Promise.resolve();
       } else {
         hasMlCapabilities = getHasMlCapabilities(request);
       }