feature #57658 [Notifier] Remove the Gitter bridge (fabpot)

This PR was merged into the 7.2 branch.

Discussion
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[Notifier] Remove the Gitter bridge

| Q             | A
| ------------- | ---
| Branch?       | 7.2
| Bug fix?      | no
| New feature?  | yes <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Issues        | Fix #52862 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT

The Gitter API does not exist anymore.

Commits
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e0a1a90a07 [Notifier] Remove the Gitter bridge

Author: fabpot

DependencyInjection/FrameworkExtension.php

@@ -2779,7 +2779,6 @@ private function registerNotifierConfiguration(array $config, ContainerBuilder $
             NotifierBridge\FortySixElks\FortySixElksTransportFactory::class => 'notifier.transport_factory.forty-six-elks',
             NotifierBridge\FreeMobile\FreeMobileTransportFactory::class => 'notifier.transport_factory.free-mobile',
             NotifierBridge\GatewayApi\GatewayApiTransportFactory::class => 'notifier.transport_factory.gateway-api',
-            NotifierBridge\Gitter\GitterTransportFactory::class => 'notifier.transport_factory.gitter',
             NotifierBridge\GoIp\GoIpTransportFactory::class => 'notifier.transport_factory.go-ip',
             NotifierBridge\GoogleChat\GoogleChatTransportFactory::class => 'notifier.transport_factory.google-chat',
             NotifierBridge\Infobip\InfobipTransportFactory::class => 'notifier.transport_factory.infobip',

Resources/config/notifier_transports.php

@@ -31,7 +31,6 @@
         'discord' => Bridge\Discord\DiscordTransportFactory::class,
         'fake-chat' => Bridge\FakeChat\FakeChatTransportFactory::class,
         'firebase' => Bridge\Firebase\FirebaseTransportFactory::class,
-        'gitter' => Bridge\Gitter\GitterTransportFactory::class,
         'google-chat' => Bridge\GoogleChat\GoogleChatTransportFactory::class,
         'line-notify' => Bridge\LineNotify\LineNotifyTransportFactory::class,
         'linked-in' => Bridge\LinkedIn\LinkedInTransportFactory::class,