Use wayland-protocols

Summary:
So far we've been copying protocol specifications from wayland-protocols
repo to kwayland repo. The main issue with copying is that we have to
keep xml files in sync manually. A better approach would be to use xml
specs straight from wayland-protocols package.

Test Plan: Compiles.

Reviewers: KWin, Frameworks, romangg, davidedmundson

Reviewed By: KWin, romangg, davidedmundson

Subscribers: davidedmundson, apol, romangg, asturmlechner, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D22216