chore: remove old slack notification (#23090)

remove old slack notification

we now have new and improved ones from posthog/charts

.github/workflows/build-and-deploy-prod.yml

@@ -12,22 +12,6 @@ on:
             - 'livestream/**'
 
 jobs:
-    slack:
-        name: Notify Slack of start of deploy
-        runs-on: ubuntu-20.04
-        if: github.repository == 'posthog/posthog'
-        steps:
-            - name: Notify Platform team on slack
-              uses: rtCamp/action-slack-notify@v2
-              env:
-                  SLACK_CHANNEL: platform-bots
-                  SLACK_COLOR: ${{ job.status }} # or a specific color like 'good' or '#ff00ff'
-                  SLACK_ICON: https://github.com/posthog.png?size=48
-                  SLACK_MESSAGE: 'Production Cloud Deploy Beginning :rocket: - ${{ github.event.head_commit.message }}'
-                  SLACK_TITLE: Message
-                  SLACK_USERNAME: Max Hedgehog
-                  SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }}
-
     sentry:
         name: Notify Sentry of a production release
         runs-on: ubuntu-20.04