Define ownership of edid in output and do not leak it

Summary: Valgrind showed that in some cases we were leaking the edid in tests.

Test Plan: valgrind --leak-check=full bin/testkwaylandbackend

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D14428