Chore: Remove failed and canceled agent replies in note comments

What does this MR do and why?

This MR removes the error_text for failed and canceled statuses on agent replies if it is replying on a note (meaning the note session bar should be present).

References

• Related GitLab Work Item: #630645 (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.
• Make sure you have docker and gitlab runners up.

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

1. 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/.
2. The first place: Work Items. Go to a Work Item in which you have the Duo Agent Platform (DAP) enabled.
3. Start a new comment and tag an agent (ex: @ duo developer)
4. Note that a session starts, the session bar displays.
5. Select that Session (click the bar) and Cancel the session (the cancel icon on the right hand side of the session details at the top).
6. Notice that the Session has the updated canceled state message. There should be no reply.
7. Repeat steps 1-4. When the Session is running, stop your local docker instance (for me it's colima stop).
8. Notice that the Session has updated to the failed state message. There should be no reply.
9. In the second place: Merge Requests. Go to a Merge Request in which you have DAP enabled.
10. Repeat steps 3-8.
11. In the third place: Merge Requests - Diffs. Go to your MR that you are in, and go to the diffs section.
12. Repeat steps 3-8 in normal mode and with rapid diffs.
13. Notice that the padding for threaded replies applies for diffs.
14. Feel free to also regression test steps 1-12 with the feature flags enabled (above) and use the master branch to compare.

MR acceptance checklist

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Related to #630645 (closed)