[libinput] Remove workaround for mouse configuration

Summary:
With the Wayland enabled Mouse KCM we do not need the workaround
to control button mapping and acceleration anymore.

Depends on D11468

Test Plan: Compiles.

Reviewers: KWin, graesslin

Reviewed By: KWin, graesslin

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D11472