Mattermost-server: Remove utils.displayTime in favour of FormattedTime component

[mattermod]

The displayTime function in utils/utils.jsx manually formats a date, but we can use the FormattedTime component from react-intl to do this for us. That component is also better localized than the function.

That function should be removed and replaced with a FormattedTime

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JIRA: https://mattermost.atlassian.net/browse/MM-18582

[niklabh]

Here's a PR: https://github.com/mattermost/mattermost-webapp/pull/3693

[niklabh]

Here's a new PR: https://github.com/mattermost/mattermost-webapp/pull/4117

[saturninoabril]

Thank you @niklabh for your contribution!