minor #15907 [Mailer] Remove SwiftMailer contents (javiereguiluz)

This PR was merged into the 5.3 branch.

Discussion
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[Mailer] Remove SwiftMailer contents

We started deprecating Swift Mailer in Symfony 4.3 docs ... so I propose to do this:

1) Remove the Swift Mailer contents in 5.3 and up ... but keeping the doc pages to avoid errors and confusions.
2) In 6.0 and up, remove those pages and redirect to the new Symfony Mailer equivalent pages.

Commits
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5c87228 Remove SwiftMailer contents

Author: javiereguiluz

bundles.rst

@@ -28,7 +28,6 @@ file::
         Symfony\Bundle\SecurityBundle\SecurityBundle::class => ['all' => true],
         Symfony\Bundle\TwigBundle\TwigBundle::class => ['all' => true],
         Symfony\Bundle\MonologBundle\MonologBundle::class => ['all' => true],
-        Symfony\Bundle\SwiftmailerBundle\SwiftmailerBundle::class => ['all' => true],
         Doctrine\Bundle\DoctrineBundle\DoctrineBundle::class => ['all' => true],
         Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle::class => ['all' => true],
         // this bundle is enabled only in 'dev' and 'test', so you can't use it in 'prod'