analytics: Remove unused click handler in populate messages by client.
analytics: Remove unused click handler in populate messages by client.

Removes a click handler in `populate_messages_sent_by_client` for
anchor links that start with a hash.

I think this goes back to when there was a sidebar navigation on
the stats page, which no longer exists. The only anchor link in
the current html is to the help center documentation and not part
of the Plotly charts.

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