Remove DDEV override for Symfony Mailer

Problem/Motivation

DDEV now automatically adjusts Symfony Mailer configuration via settings.ddev.php. This is documented in https://ddev.readthedocs.io/en/stable/users/usage/developer-tools/#email...

If you’re using SMTP for outgoing mail—with Symfony Mailer or SMTP modules, for example—update your application’s SMTP server configuration to use localhost and Mailpit’s port 1025.

For Drupal 9+ settings.ddev.php overrides the Symfony Mailer sendmail configuration to use Mailpit.

This means the Symfony Mailer default config will be automatically overridden in ddev environment and mails are redirected to mailpit.

This means we can remove the following files from the Base Recipe:
config/symfony_mailer.mailer_transport.ddev_smtp.yml
config/symfony_mailer.settings.yml