[wayland] Drop initSurface method in XdgShellClient
Summary:
XdgShellClient can represent either a xdg-toplevel or xdg-popup. Therefore,
template initSurface method is no longer needed.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D24196