minor symfony#60416 [FrameworkBundle] remove no longer used service definition (xabbuh)

This PR was merged into the 6.4 branch.

Discussion
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[FrameworkBundle] remove no longer used service definition

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

In symfony#59781 it was forgotten to remove the definition when an alias with the same name was introduced.

Commits
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5940258 remove no longer used service definition

Author: nicolas-grekas

src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer.php

@@ -45,7 +45,6 @@
                 tagged_iterator('mailer.transport_factory'),
             ])
 
-        ->set('mailer.default_transport', TransportInterface::class)
         ->alias('mailer.default_transport', 'mailer.transports')
         ->alias(TransportInterface::class, 'mailer.default_transport')