[wayland] Fix teardown order

Summary:
Valgrind flags an error on teardown.

EventQueue has a pointer to ConnectionThread internally
Registry has a pointer to the EventQueue internally

teardown order needs to be

Registry
EventQueue
Connection

registry was explicitly deleted before connectionthread already, we just
need to put event queue in the right place.

Test Plan: Ran kwin_wayland nested in valgrind

Reviewers: #kwin, cblack, apol

Reviewed By: cblack, apol

Subscribers: zzag, apol, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28668