Tests: remove prepDb workaround

Previously, the `prepareDatabase` method would directly modify the database, booting the app in the process. This would prevent any extenders from being applied, since `->extend()` has no effect once the app is booted.

Since the new implementation of `prepareDatabase` simply registers seed data to be applied during app boot, the workaround of sticking this seed data into `prepDb` is no longer necessary, and seed data common to all test cases in a class can be provided in `setUp`.

When needed, app boot is explicitly triggered in individual test cases by calling `$this->app()`.

tests/integration/extenders/CsrfTest.php

@@ -79,8 +79,6 @@ class CsrfTest extends TestCase
                 ->exemptRoute('users.create')
         );
 
-        $this->prepDb();
-
         $response = $this->send(
             $this->request('POST', '/api/users', [
                 'json' => [