Mattermost-server: Remove/fix duplicate uses of post-list

[mattermod]

This issue was found by the aXe Chrome extension for finding WCAG issues. In order to successfully complete this issue, you'll need to make sure to test using the tool and ensure that all of the warnings covering the components scoped below are cleared. You can find more information on the issue at the link below:

We are commonly using the same id tag on html elements repeatedly. We need to make sure we are using unique ones throughout the application.

The post-list id is being used by multiple components, we’ll need to remove the duplication and fix the CSS styles that are using the id.

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JIRA: https://mattermost.atlassian.net/browse/MM-20271

[M-ZubairAhmed]

can i take this ?

[M-ZubairAhmed]

As per discussion with @devinbinnie, Following are the findings :

This issue doesnt crop up in aXe as evident from the following screen shot

In the webapp code base there is no duplication of id post-list

[devinbinnie]

We've determined this has been fixed, closing. Thanks to @M-ZubairAhmed for the assistance :)