[platforms/hwcomposer] Remove code for turning screen on and off

Summary:
Previously hwcomposer backend used android lights module for turning
screen on and off, however now that powerdevil code supports the setting
brightness. Remove this code.

Reviewers: KWin, graesslin

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D2424