Remove duplicate buttons

What does this MR do?

Fix regression and remove duplicate buttons:

• jump to next discussion
• resolve this in a new issue

The implementation is the same as previous MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29779

Test Case

1. Navigate to Merge Requests > [select a MR] > Changes
2. Hover on any line of the code to trigger the speech bubble icon and click on it.
3. Comment box will appear. Leave a random comment and click the "Comment" button to submit
4. Switch to the Discussion tab

Unresolved discussions looks like this:



Resolved discussion looks like this:

Note

You may noticed the style of the button is a bit off. That's because the buttons are broken as mentioned in these issues:

• https://gitlab.com/gitlab-org/gitlab-ce/issues/64569
• https://gitlab.com/gitlab-org/gitlab-ce/issues/64464

One these issues are solved, the buttons would look as expected. So for this ticket, the buttons will look something like this:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #64160 (moved)