chore: remove slack notifications to infra-release-notify

[jmlrt]

This commit is removing the Slack notifications to
#infra-release-notify channel.

Following elastic/observability-robots#1002,
the ownership of o11y Helm charts should move to o11y team.

cc @elastic/infra-release

[mergify]

This pull request does not have a backport label. Could you fix it @jmlrt? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[jmlrt]

👋🏻 @mdelapenya, is there something to do to fix the 2 failing tests, or should we admin-merge? In addition, is there a need to backport to other branches?

[mdelapenya]

The errors are not related to this PR, and they are in upstream (we are on it).

About the backports, we do run the Helm charts tests for main (== 8.1.0-SNAPSHOT), main-1 (8.0.0-SNAPSHOT) and main-2 (7.17 and 7.16), so we still need this backported as this is a multibranch pipeline (tip: we use the mbp suffix everywhere)

[jmlrt]

Thanks 👍🏻
I've added the backport labels and will let you merge when tests are fixed upstream then.

[mdelapenya]

Thanks 👍🏻 I've added the backport labels and will let you merge when tests are fixed upstream then.

I think we are good to merge even though the upstream tests are broken, as we are in the middle of stabilising them.

Thanks for your help here