minor #17337 [3.0] [Bridge] [Swiftmailer] Removed non-existent namesp…

…ace from composer.json autoload section (paradajozsef)

This PR was submitted for the master branch but it was merged into the 3.0 branch instead (closes #17337).

Discussion
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[3.0] [Bridge] [Swiftmailer] Removed non-existent namespace from composer.json autoload section

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

After PR #13046 Symfony\Bridge\Swiftmailer\ ns not exists.

Commits
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ecf4591 Removed non-existent directory from composer autoload

composer.json

@@ -91,7 +91,6 @@
             "Symfony\\Bridge\\Doctrine\\": "src/Symfony/Bridge/Doctrine/",
             "Symfony\\Bridge\\Monolog\\": "src/Symfony/Bridge/Monolog/",
             "Symfony\\Bridge\\ProxyManager\\": "src/Symfony/Bridge/ProxyManager/",
-            "Symfony\\Bridge\\Swiftmailer\\": "src/Symfony/Bridge/Swiftmailer/",
             "Symfony\\Bridge\\Twig\\": "src/Symfony/Bridge/Twig/",
             "Symfony\\Bundle\\": "src/Symfony/Bundle/",
             "Symfony\\Component\\": "src/Symfony/Component/"