Remove X11Compositor requires compositing check
Summary:
With the split of the Compositor class in X11 and Wayland it is unnecessary
to check in X11Compositor if compositing is required since on X it never is.
Test Plan: Compiles.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D23032