Use extensible profiles instead of the display name

[turt2live]

We use the display name so we can communicate metadata between bots without flooding the room or requiring permissions in rooms. This helps bots optimize what servers they should expect replies from so they don't accidentally consider a server down.

Extensible profiles (https://github.com/matrix-org/matrix-doc/issues/489) are a much better solution.