Remove non-existing re-export from helper-addon blueprint

The blueprint for an addon's `app/helpers/foo.js` contains a re-export of a named export of `addon/helpers/foo.js` which does not exist, as it only has a default export.

FWIW, Embroider is constantly complaining about this (rightly).

(cherry picked from commit 7aa8233)

blueprints/helper-addon/files/__root__/__path__/__name__.js

@@ -1 +1 @@
-export { default, <%= camelizedModuleName %> } from '<%= modulePath %>';
+export { default } from '<%= modulePath %>';

node-tests/fixtures/helper/helper-addon.js

@@ -1 +1 @@
-export { default, fooBarBaz } from 'my-addon/helpers/foo/bar-baz';
+export { default } from 'my-addon/helpers/foo/bar-baz';