Remove Session Status comments from Agent Mentions

What does this MR do and why?

This MR removes the generated status comments when an agent is mentioned.

References

• Related GitLab Work Item: #613039 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

For DAP/General Setup

• General DAP: https://docs.gitlab.com/development/duo_agent_platform/
• Assigning Duo to a group: https://docs.gitlab.com/development/ai_features/#run-gitlabduosetup-script
• Make sure you are in SaaS mode with export GITLAB_SIMULATE_SAAS=1 set in your env.runit file in your local gdk.

Adding Sessions

1. A: If you see no Sessions, you can trigger one that displays a Pipeline/Job by going to an Issue within your Duo enabled project and clicking the Generate MR with Duo button. It should trigger a new session that you can open up.
2. B: You can also run the following query bundle exec rake "gitlab:duo_workflow:populate[50,20,1,<<YOUR_TEST_GROUP_PATH_HERE>>]" to create new agent sessions. Refresh the page. Make sure the group you are testing in has Duo assigned (see DAP setup above).

The actual testing

0. Note: For this you will need to test in 3 places. Make sure you have the following 2 FFs enabled: note_agent_session_bar and clear_action_cable_loader. You can always use your local rails console or http://gdk.test:3000/rails/features/.
1. The first place: Work Items. Go to a Work Item in which you have the Duo Agent Platform (DAP) enabled.
2. Start a new comment and tag an agent (ex: @ duo developer)
3. Note that a session starts, the session bar displays, but no status comment is shown.
4. In the second place: Merge Requests. Go to a Merge Request in which you have DAP enabled.
5. Repeat steps 2-3.
6. In the third place: Merge Requests - Diffs. Go to your MR that you are in, and go to the diffs section.
7. Repeat steps 2-3 in normal mode and with rapid diffs.
8. Feel free to also regression test steps 1-7 with the feature flags enabled (above) and use the master branch to compare.

MR acceptance checklist

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Related to #613039 (closed)