Mattermost-server: Remove call to `openLhs` from SidebarChannel render method

[mattermod]

In the SidebarChannel component code that handles showing the tutorial tip for the Town Square and Off-Topic channels, there's a call to the openLhs action which is not allowed in React. This triggers a warning.

The openLhs call should be moved to happen after the render.

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JIRA: https://mattermost.atlassian.net/browse/MM-21052

[M-ZubairAhmed]

I am taking this one

[hanzei]

Thanks @M-ZubairAhmed :+1:

[jasonblais]

@M-ZubairAhmed You took another two help wanted tickets, but a quick reminder that you had previously also claimed this one. :) Big thanks for your help!