Remove composite reset timer
Summary:
To streamline Compositor code more remove the composite reset timer. The two
times it was used we can either use a singleshot timer instead or connect the
call to a different signal in the X11 backend.
Long term goal is to have a well structured init of the Compositor such that
we can call directly instead.
Test Plan: Manually in X and Wayland nested session.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: zzag, kwin
Tags: KWin
Maniphest Tasks: T11071
Differential Revision: https://phabricator.kde.org/D22270