jamiaccount: remove too big payload for request

Because the encoded avatar can be greater than 64k, a SIP message
will fail, and the trust request may not be sent.

https: //git.jami.net/savoirfairelinux/jami-client-qt/-/issues/1491
https: //git.jami.net/savoirfairelinux/jami-client-android/-/issues/1537
Change-Id: Ieba2db521a3c7e72890be75d3578f93e496dc968