minor #15205 [Notifier] Remove variable (OskarStark)

This PR was merged into the 5.3-dev branch.

Discussion
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[Notifier] Remove variable

Commits
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2204e13 Remove variable

Author: OskarStark

notifier.rst

@@ -155,7 +155,7 @@ Service     Package                           DSN
 Discord     ``symfony/discord-notifier``      ``discord://TOKEN@default?webhook_id=ID``
 FakeChat    ``symfony/fake-chat-notifier``    ``fakechat+email://MAILER_SERVICE_ID?to=TO&from=FROM``
 Firebase    ``symfony/firebase-notifier``     ``firebase://USERNAME:PASSWORD@default``
-Gitter      ``symfony/gitter-notifier``       ``GITTER_DSN=gitter://TOKEN@default?room_id=ROOM_ID``
+Gitter      ``symfony/gitter-notifier``       ``gitter://TOKEN@default?room_id=ROOM_ID``
 GoogleChat  ``symfony/google-chat-notifier``  ``googlechat://ACCESS_KEY:ACCESS_TOKEN@default/SPACE?thread_key=THREAD_KEY``
 LinkedIn    ``symfony/linked-in-notifier``    ``linkedin://TOKEN:USER_ID@default``
 Mattermost  ``symfony/mattermost-notifier``   ``mattermost://ACCESS_TOKEN@HOST/PATH?channel=CHANNEL``