Call workspaceEvent and updateX11Time only once per event

Summary:
On Wayland processXcbEvents calls workspaceEvents and updateX11Time but this
is already done in the native event filter.

Test Plan:
Manual test shows Xwayland still works and constant calls to
XcbEventFilter::nativeEventFilter are processed.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D14215