[BB-3825] Fix: Hide new post indicator on thread open

Description

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    1. Description
      Fixes the removal of the new post indication in unit discussion once a thread has been opened.

When an unread thread is clicked, the user expects the blue margin highlight to be removed. However, it is not removed even after opening the thread a number of times. This behaviour is different from that shown in the Discussion tab where the margin highlight is removed. See below

![simplescreenrecorder-2021-03-05 (2)](https://user-images.githubusercontent.com/13065283/110171132-507cde00-7e0c-11eb-9a0c-e61816aad33a.gif)

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    1. Testing Instructions

  • Login to the LMS with account A

  • Open a unit with a discussion block. Make a few contributions to the discussion by posting a few comments

  • Logout and then login with a different account (account B) that is enrolled to the same course.

  • Visit the same unit. You should be able to see the posts made by account A highlighted with a blue left border.

  • Click on one post to open the thread. This should open a view of the thread.

  • Click on All Posts to go back to the list of posts. Confirm that the highlight on this thread has been removed.

  • Open other threads to confirm this fix.

Done
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Assignee

Sarina Canelake

Reporter

Open Source Pull Request Bot

Labels

Contributor Name

Paul Aswa

Repo

edx/edx-platform

Customer

Github Lines Added

19

Github Lines Deleted

1