Don't send our own notifications

Summary:
They were silent anyway and are not really useful
BUG: 402490

Test Plan: I don't see the MPRIS notification in the plasmoid any more

Reviewers: KDE Connect, albertvaka

Reviewed By: KDE Connect, albertvaka

Subscribers: kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D17776