Remove current_user from awareness payload

What does this MR do and why?

Based on feedback in this MR, we want to remove the current_user from the awareness payload. This is not a breaking change, because it isn't used anywhere yet.

We remove the current_user from the payload every time the payload is transmitted. We do not need to display the avatar for the current_user. In addition, the size of the avatar image is reduced a bit.

How to set up and validate locally

Added and modified an existing spec to cover the changes.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.