"to" is duplicated when sending messages in "sendCallMessage"

[fancycode]

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Steps to reproduce

1. Setup external signaling.
2. Start typing in chat.
3. Look at messages being sent for the typing indication.

Expected behaviour

The session id the recipient should only be included once.

Actual behaviour

The session id of the recipient is used in the recipient and also included in the data: https://github.com/nextcloud/spreed/blob/ff123623e76de5ba85fcd97898c07b305d5ca3ab/src/utils/signaling.js#L932-L941

It should not be part of data as the message will only be sent to the session in recipient and the recipient knows the own id.